Try contacting these guys:
Maccsteam
Web Site:
www.maccsteam.comE-mail: mike@maccsteam.com
Phone: 01625 619784
Address: 79 Victoria Road, Macclesfield, Cheshire, SK10 3JA
Excelent boilers supplied either bare or with fittings
Mainsteam Models
Web Site:
www.mainsteam.co.ukE-mail: sales@mainsteam.co.uk
Phone: 07940 306945
Bespoke manufacturer of plant and accessories.
Monahan Steam Models
Web Site:
www.monahansteammodels.comE-mail: Enquiries@monahansteammodels.com
Address: 205 De Anza Blvd. #121, San Mateo, Ca. 94402
Check out the web site for superb off the shelf boilers.
Steam Fittings
Web Site:
www.steamfittings.co.ukE-mail: sales@steamfittings.co.uk
Phone: 01341-280637
Address: 36 Elder Drive, Daventry, Northants, NN11 5XE
Everything you could need to stick all the bits together.
Anton (Fabrice Bretagne)
Web Site:
http://fabrice.bretagne.club.frE-mail: fabrice.bretagne@club-internet.fr
Phone: (33) 05.46.33.21.35
John Hemmens
Web Site:
www.steamengines.co.ukE-mail: enquiries@steamengines.co.uk
Phone: 01757 289664
Address: 28 Breighton Road, Bubwith, Selby. North Yorkshire, YO8 6DQ.
Again excellent quality off the shelf boilers and plant.
Marten, Howes and Baylis
Web Site:
www.model-steam-boats.co.ukE-mail: Martenhowesbaylis@btinternet.com
Phone: 01634 233146
Address: 216 Bredhurst Road, Wigmore, Gillingham, Kent, ME8 0RD
The Model Dockyard
Web Site:
www.model-dockyard.comE-mail: via the web site contact page.
Phone: 01872 261755
Address: 17 Tremorvah Barton, Tregolls Road, Truro, Cornwall, TR1 1NN
General model boat suppliers including steam items.
Westbourne Models
Web Site:
www.westbourne-model.co.ukE-mail: saleswestbourne@btconnect.com
Phone: 01202 763480
Address: 41 Seamoor Rd, Westbourne, Southbourne, Dorset, BH4 9AE
Again a general model supplier including steam plant and accessories.
That should at least give you an idea of what's out there and give you something to be looking at. Any other questions don't hesitate to ask.