...you can probably scrounge up some free spacers from old cog clusters at a bike co-op or from discarded cog clusters. You appear to be describing a Shimano Hyperglide freehub, and there's a lot of stuff bouncing around that will fit. You need enough of them so you can get your single cog to run more or less in the center of the freehub. or wherever the chain line is straightest to your crank chain wheel.

You also need enough spacers so that when you tighten the lock ring, there is pressure on the stack, so stuff does not move around back there.