Is there a reason why you can't take your own? Cos I really can't think of anywhere but Spanish_80 might he's local.

May be a very (very) long shot But a few years back I had to hire a wheelchair for my mother who broke her ankle out there. If I remember correctly the place we hired from was on or near the Plaza Eoropa. Sorry its so vague, but it's an episode we wanted to forget

Meanwhile perhap the link below may be of some help

http://www.salou-tourist-guide.com/en/general/salou-tourist-information.html

i hired a wheelchair in june for my mother. we got it through the hotel, maybe you could try
the hotel you are staying at to see if they do the same.