Gator Checks of Bullet Swaging Supply, Inc. has no website, but you can email Larry Blackmon at leblackmon@colla.com and from my experience he's great to deal with.
Also getting to your question on the gas checks, Gator Checks are offered in two .45 sizes. Both accept the same shank size, if I recall correctly the ID is .426, the check for the .458 rifle is slightly thicker than the other .45 for pistol. Their prices beat any I've seen for Honady and I cannot see any compromise of quality or accuracy, and have heard many others on forums swear by these checks. Hope this helps a bit