Froggie, back in the dinosaur days when only fishermen had nets and spiders had webs, I picked up this cute little rook rifle in 300 Rook. Closest brass was 32 Long Colt so an operation was performed. It was actually possible to find an occasional box of ammo back then and I got one. In the modern age Buffalo Arms came along with a mold for a little 300 bullet so now I needed more brass. Took me several large gunshows to find a collector with a box of matching factory ammo. Was not inexpensive but necessary. It may take you a while now but at least you have many more possibilities for searching. Good luck.

A seller on Gun Broker has 188 once fired .32 Colt cases up for sale $50

If you’re looking for loaded ammo, Buffalo arms often has it. Currently they have some black powder loads.

They also have brass made from 32 S&W
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If you can find people to part with it, 25-20 SS brass works. So cases with split necks are often long enough.

To each his own! I don't find it to be an onerous task. On the contrary, such tasks are part of what drew me to this hobby in the first place. I also take it as a challenge to thwart the Big Ammo company's (to include BACO and others of that ilk) efforts to limit my shooting of vintage rifles.

Sometimes such work as converting brass to other configurations isn't a means to an end, rather the end in and of itself.