it is... and well worth the effort.

the Rockshox 409 fork i have here uses an insert into a plain bore.... it's a 20mm thru-axle type.
if yours is a similar design, just in 15mm, then an adapter could be used.

and no matter what you find available.. you'll need to know the pitch of any threads involved.... most axles have the pitch on them.
i recall a list of at least 9 "common" pitches for 4 diameters of thru-axles.
that site 13ollochs linked looks promising.
ebay only shows a bunch of "other way" offerings.

personally, i'd still get the correct hub, and do it right.