For other objects I know no other way than GUIScripting.
tell application "Numbers" to tell document 1
set sheetNames to name of sheets --> {"Budget", "Transactions"}
repeat with aSheet in sheetNames
tell sheet aSheet
set nbTables to name of tables
--> {"Résumé par catégorie"} in sheet 1
--> {"Transactions"} in sheet 2
set iWorkItems to iWork items
repeat with anItem in iWorkItems
properties of anItem
(* in sheet 1
--> {opacity:100, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", class:shape, reflection showing:false, background fill type:no fill, position:{0, 47}, object text:"INSTRUCTIONS : saisissez votre budget pour chaque catégorie dans le tableau Résumé par catégorie ci-dessous.
Saisissez les transactions dans la feuille Transactions pour comparer vos dépenses réelles avec votre budget.", width:503, rotation:0, reflection value:0, height:48, locked:false}
--> {reflection showing:false, class:line, end point:{503, 91}, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", position:{0, 91}, reflection value:0, height:0, width:503, start point:{0, 91}, locked:false, rotation:0}
--> {reflection showing:false, class:line, end point:{503, 43}, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", position:{0, 43}, reflection value:0, height:0, width:503, start point:{0, 43}, locked:false, rotation:0}
--> {locked:false, cell range:range "A1:D11" of table 1 of sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", column count:4, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", header column count:1, footer row count:1, class:table, header columns frozen:false, position:{0, 452}, filtered:false, header rows frozen:true, width:503, name:"Résumé par catégorie", selection range:range "A1:D11" of table 1 of sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", header row count:1, height:247, row count:11}
--> {position:{15, 142}, class:chart, width:189, height:189, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", locked:false}
--> {position:{303, 143}, class:chart, width:199, height:152, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", locked:false}
--> {opacity:100, parent:sheet 1 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", class:text item, reflection showing:false, rotation:0, background fill type:no fill, position:{0, 0}, object text:"budget mensuel", width:503, reflection value:0, height:42, locked:false}
*)
(* in sheet 2
--> {table 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", line 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", shape 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", line 2 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", text item 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F"}
--> {locked:false, cell range:range "A1:D27" of table 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", column count:4, parent:sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", header column count:0, footer row count:0, class:table, header columns frozen:false, position:{0, 112}, filtered:false, header rows frozen:true, width:504, name:"Transactions", selection range:range "A1:D27" of table 1 of sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", header row count:1, height:602, row count:27}
--> {reflection showing:false, class:line, end point:{503, 91}, parent:sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", position:{0, 91}, reflection value:0, height:0, width:503, start point:{0, 91}, locked:false, rotation:0}
-> {opacity:100, parent:sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", class:shape, reflection showing:false, background fill type:no fill, position:{0, 47}, object text:"INSTRUCTIONS : saisissez vos données dans la Transactions ci-dessous. Classez chaque transaction
dans une catégorie puis consultez la feuille Budget pour comparer chaque catégorie avec votre budget.", width:503, rotation:0, reflection value:0, height:48, locked:false}
--> {reflection showing:false, class:line, end point:{503, 43}, parent:sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", position:{0, 43}, reflection value:0, height:0, width:503, start point:{0, 43}, locked:false, rotation:0}
--> {opacity:100, parent:sheet 2 of document id "F237BB81-FAEC-4424-91FA-FD34CD74E29F", class:text item, reflection showing:false, rotation:0, background fill type:no fill, position:{0, 0}, object text:"opérations", width:503, reflection value:0, height:42, locked:false}
*)
end repeat
end tell
end repeat
end tell