Leather choice

What leather does everyone use for their miniature tack? I'm looking into making some for my 1:18 scale and have tried some but it won't skive down.

Any suggestions?

For small scale tack, or anything 1:12 or less really, I prefer fake leather, adapted slightly before cutting - you can peel the foamy/fabric backing off, leaving just a very fine layer of leather-effect plastic. Skiving with half the effort and no sharp things near fingers!
This also has practical advantages : it glues better than real leather, and you can get really flat neat folds and joins for your billets and keepers. You can age it with paint effects, draw on stitch marks. And one of the best things is that it's flexible and stretchy and soft - you can glue your buckles and keepers firmly in place for neatness, and just pull the bridle/halter on over the ears without having to make working buckles and do them up every time.
I've got a couple of big sheets in black and medium brown I bought in a fabric shop about twenty years ago and am slowly working my way through, but if you want specific or unusual colours or textures then try charity shops (or thrift stores, op shops, goodwill - whatever you have in your country!) for old synthetic leather handbags which can be 'skinned' and recycled into tack.