You probably have either a 1.5 or 2.2kw spindle. If so, it probably uses either ER16 or ER20 collets. Measure the collet. An ER16 measures about 17mm across at the widest point and about 27mm long. An ER20 measures about 21mm across the widest point and 31mm long.
Once you determine which you have, order Imperial size collets from maritool.
I ordered a 2.2kw (3hp) spindle with ER20 collets on my JCut 6090A and I use 1/8", 1/4" and 1/2" collets. I doubt you can use the 1/2" in ER16, but I'm sure you could use a 1/4".
Mine came with a 6mm collet. Too small for 1/4" shank tools. I had to buy them too. I went ahead and bought a couple of extra nuts too. That way I don't have to keep snapping the collets in and out of the nut every time I wanted to change from a 1/8" to 1/4" or vice versa.