Classic cast is only threaded for 1-1/4" so only lee dies will fit. Other companies 50 BMG use 1-1/2" dies.
I have the Lee Classic Cast and also have a custom neck sizer die made by Lee for my chamber. Lee also has 416 Barrett dies.
One thing I did was to polish the inside of the dies with Flitz on a bore mop in a cordless drill.
A similar setup with Hornady or RCBS will cost 3 times as much. But they are a heavier duty setup. I don't full length size most of the time so the HD part of the bigger presses isn't as big a consideration.
I got mine in the US from FS Reloading and shipped to the US, but many stores also ship to Canada.
Edit: Just looked it up, the Classic Cast 50 BMG kit WITH dies is $188 plus shipping. RCBS dies alone will be over $300 and you can get the RCBS 50 BMG kit for $600 US.
Or you can get the new Dillon multi station 50bmg for $1k without dies, primer seater, etc. ($800 for the Dillon carbide sizer itself)