I've heard after market are either hit or miss on reliability and the originals (if you can find them) are real pricey. I haven't seen so many holsters, but linked one below, might just want to search GB for "225 holster" and see what you get.
CDNN should have magazines for the P225/P6
Holsters I've not looked for. I've got a P6, it came with a leather on the belt holster with a thumb snap for retention. I've never worn it