Most knife supply catalogs sells the cut out leather disks by the dozen. I also used to buy them in bags of 100.
Use slow cure epoxy, and glue up while stacking on the tang ( wear rubber gloves). Clamp the pommel on snug, and wipe off any excess resin. Sand the leather and pommel to shape. Treat with edge dressing and buff with carnuba or other hard wax.
If you plan on doing this more than once, here is a great trick:
I have a mandrel made from a bolt that I use to stack and glue the disks on. The bolt is a 6" long, 1/2" bolt that I ground flat to 1/4" thick. With two washers an a 1/2" nut, it makes a great leather handle assembly tool. I use it to assemble elephant hide and birch bark handles. (Which reminds me that I need to make some more. I may try and shoot a tutorial.) This allows glue up and rough shaping off the knife.... which is a lot neater. Coat the bolt with wax to prevent it from being epoxied to the leather handle. After pre-shaping the handle ( and grinding off all the excess dried epoxy), epoxy the handle on the knife tang, with the pommel clamping it firm. Then do the final shaping and buffing.