You may want to consider a 45. I haven't noticed a .455 for sale in a while. I have several 1911's but by no means am I an expert so I'm wondering if the barrel and mag can be changed over?

Of course if you're wanting a true British .455 expect to pay big time and maybe search for a long time.

All I see on GB are a couple of collector magazines for $600 ea (auction), a nickle plated 1911 and this one that is a very poor specimen that's been re-blued, stippled frame for texture and after market grips. This auction house gets big money too on what they sell.

If you want to watch it here it is. Good luck with your search.

https://www.gunbroker.com/item/964985903