Hi Shady
Yes there are number holders with suction cups and you may be able to buy one on the day, but you if you contact Windsor Canoe Club they might sell you one or let you borrow one, just Google the Clubs web site and contact the club secretary.
If not I am the Chair for the PNSW Marathon Technical Committee and can organise to get you one of ours which will cost you a whopping $12.
Cheers
Tom.B