From another post, I found a link to a guy in the US who sells check valves much cheaper than the Mazda ones. I have ordered a set for myself, £14 odd.
http://www.clubrx.org/default.asp?id=8&ACT=5&content=26&mnu=8
He claims they are better than the stock Mazda ones, but at the price, you could replace them regularly anyway if they fail.
Yeah i have them on mine, cant tell you how good they as my car throw a wobbly when the solonoid broke lol, took a few days to get here nice bloke to deal with as well.
We should have a sticky link of useful purchases?
Cheers
Gav