[Nyles]

.455 Auto ammo is one of the few truly impossible to find calibers out there. I have a single round from 1941 that I bought at a gunshow for 8$. That said, its very easy to cut an extractor groove in .45 Colt cartridges and form them to the appropriate size, and you can even buy pre-formed brass. .455 Webley isn't bad, most gun shops that cater to collectors have it.

I've managed to shoot most of my guns over the years, either with very expensive ammo from specialty manufacturers (Fiocci is the big one, also Precision Cartridge Inc, Old Western Scrounger, even Norma or Hornady for the only slightly rare stuff) or using surplus ammo. In fact, so far the only stuff that eludes me is .455 Auto, 8mm Nambu, 7.65mm Longue, 8 x 50mm Mannlicher. I haven't tried with 10.4mm Italian or .450 Boxer Henry, but Fiocci loads 10.4mm so that won't be an issue. .450 is gonna be more of a challenge, but likely doable.

The lack of decent collector's gun shops in my city and the hassles with shipping ammo in Canada are the two biggest factors. When I'm in Edmonton I have a buddy who used to work for the big shop there and he gets them to order specialty stuff for me, its just a question of paying.