CQ - I haven't seen it in pet shops, only vets - but try some of the bigger ones ... (pet shops that is!)

Peeing is different to spraying - spraying is marking territory done by whole toms, and desexing will stop that behaviour. Peeing though is behavioural and isn't related to gender. MrsS' thing about mixing dirt in with the litter is a good thing, it's worth doing whenever you change litter brands / types to get them used to it ..

Good luck!