What determines collet compatibility is the shank diameter — that tool has a 1/4" shank and will work w/ a 1/4" collet (included w/ a VFD or our other Shapeoko spindle options).
See:
ER-11 collets are available in up to 8mm from 3rd parties — I bought one from Maritool (because I found their site easy to navigate/understand):
and various other vendors offer them.
As noted above, all of our tooling has either a 1/4" or 1/8" shank (which is what determines collet compatibilty), so you can use any of our tooling w/ the VFD as it is, save for the McFly #603E:
(which would want the 8mm ER-11 collet linked above)