When I've done this, for guide maps, notices etc., I've simply encapsulated an ordinary sheet of paper off my printer.
We have an encapsulating machine at the office, but I would think printers would be able to source someone, also.

If it's just numbers, to put on the back, any shop that deals in the paraphanalia that surrounds horse riding stocks, or can get, numbers on flexible plastic, with holes already punched to tie on. I imagine that any competitive sport would have the same requirement, and stock them