Actually, the place to get a Gatling isn't Dillon. Here are two places.
[url=http://www.gatlinggun.net/]Gatling Gun Company[/url] makes replica original-style Gatlings using precharged black-powder "chambers". Prices start at $4810. Since these are BP only, no FFL is required.
[url=http://www.gatlingguns.net/]RG-G Inc.[/url] makes miniature replicas in .22LR. Prices run from $58 (plans only) to $10,900 (complete, finished, fully polished Gatling). The finished firearms, which I think the club would have to buy on a plain old Form 4473 (a group can't manufacture a firearm for personal use, from my limited understanding of BATF regs), start at $4800.
Dillon makes Miniguns, but since they are electric-motor-cranked machine guns made post-1986, they must be purchased by government/military/LEO only. I don't know enough about the Class III regs to say whether a corporation or licensed dealer/mfr can buy one and hold it in the name of the club, but I don't think so.