Seems that there wasn't any on thingiverse. So I found one here https://grabcad.com/library/xt-60-female-connector-1 and made STL.
You need to drill holes with 4.5mm bit and slightly enlarge back side of holes, say 5.5-6mm bit few mm deep. This way 3.5mm bullets go in easily but you have to push/hit these all the way in so they stay secure.
Seems to fit male connector quite tightly. If it's too tight scale down by few percent.