Like most (if not all) sheridans, palmer's has rebuild kits and other necessities. Pro-team products still has several upgrades (.45 frames, armson barrels, CAR stocks, etc). Lapco still has VM to cocker barrel adapters.
As far as function goes, ya know how just about everybody copied Spyders? Well, it's my personal belief that kingman copied their basic operation from the VM. It's a stacked-tube blowback. And if Spyders are gas hogs, a VM is a herd of them.
By all reports, the trigger group is a pain to tinker on, but I haven't had mine apart yet to confirm it.
They are ridiculously/absurdly/painfully/phenomenally/(insert appropriate metaphor here) heavy, and you can feel the kick without having any air hooked up to it.
The guns and parts can be found with a reasonable amount of patience and time.
Good luck to you, and if you get one, enjoy it. As with any gun, its shortcomings will only make you a better player. Stronger, too