A lot of boat builders can do it as can a lot of "metal workers" any one who does stainless handrails etc. Also try asking in your local industrial gas suppliers (BOC supagas etc) as they can probably give you a few suggestions
I've a mate in narre warren who does it, and has helped his brother in-law build his entire 3V brewery so he has experiance. But hes on holiday at the moment. If your interested and located out that way i can get you his number tomorrow when im at work.