Used both companies in the past,

Peter dysons I think keep a handful of each in stock and I have had new bits received within a week of ordering the hammers were fine easy to work and looked great.

Blackleys I think cast a couple of times a year and when you place an order you are added to the cast, this is fine except I did have one hammer fail to cast, blackleys let me know this had happened but I did have to wait till the next cast; this is the problem when there are two shops in town and only one of them sells the right product for you. I waited a long time and when the castings finally showed up I would say they were a higher quality product, even once annealed the steel was definitely harder; lines crisper ect.. that being said while trying to punch my holes to square two homemade ( poorly made no doubt ) punches went in square and came out round... we got there in the end.