Pedersoli are probably the biggest manufacturer but they are also made by Ardesa and a couple of the lesser known Italian manufacturers. Henry Kranks have a good range which you can view in their catalogue (download in .pdf). Go to www.henrykrank.com
If you are looking for something specialised, this guy has one made by Feinwerkbau for sale. Check out his website at www.historicguns.co.uk
Regards
C-B