So, I'm about to build Arthur from Thomas and Friends, and I need the blueprints from the real engine, but don't know the best source for train blueprints. Arthur is a LMS Ivatt Class 2MT 2-6-2T engine.
It's a joke. You should describe what you have done so far to search for these blueprints. Otherwise, your response to all the replies will be 'I've already done that' which is very frustrating for people trying to help.
I've tried before to look for blueprints, but when I do, it's either the wrong class, or the right class, but low resolution blueprints, or no blueprints at all.
Have a look at the Bluebell Railways restoration of loco 84030 which is based on Evatt's 2MT design. See http://www.bluebell-railway.co.uk/bluebell/locos/84030.html The web page only has a side view but there are plenty of photos around to help out.
Its not remotely like a blueprint but I've made models from worse drawings.