Cruciform:
I'm not sure how far you want to travel, but the Superpet in London has some. I've some some provent-a-mite cans in the Superpet on the corner of Exeter Rd. and Wellington Rd. I go there to buy crix and I've always been able to spot the cans when I browse around. They are around $40

(I forget the exact cost). You can probably order some online, but I haven't looked into that so I don't know what the prices are like.