It was called a 22-10-45 so try 10 grains of black powder or as much as you can get in a case. The originals shot a .228" diameter bullet but if it is a recreation then you'll need to slug the bore. A 22 Hornet die can be used as a neck sizing die.

My books note 7gr of 3F for the 22 Maynard XL.  Also, you could likely use the loads for the 5.5 Velo Dog cartridge, although I think FL is no longer made.  My COTR notes that 8-10gr of 3F or 4F or 5-6 grains of Dupont bulk shotgun powder could be used.  The Lyman 228151 is the suggested bullet.
James Grant in his book says he had decent luck with 4.6gr of 4759 (also discontinued) but you might be able to substitute 5744 instead.
I have a 22 Maynard XL also and have been looking around for load data and a mould.  Let me know your results.  The Maynard catalogs made great claims for the cartridge.

Ron, I'll go out on a limb and suggest either 2 grains of Unique or 3 grains of 4227 as a starting point. Increase .1 grain at a time until you get that supersonic crack like a 22 LR high velocity. Then back off to keep it subsonic.

I spoke with someone who shoots a 22 Maynard centerfire and he shoots 1.7 grains of Trailboss. Says it is a mild load and fills the case enough to prevent double loading.