Hi Thomas, The first thing I would do is find and join a local ME club ! Where abouts are you ? Talk to the boiler inspector and get his advice or help. It is not impossible to make your own boiler and with the help of your club they may have the gear to do it.  I made this mistake 35 years ago, it can be a steep learning curve.

Removing the boiler very much depends on your skills and equipment. Depending on what the trouble is will dictate if it can be repaired. Having a new one built will be very costly and there may be a long waiting list. Has the boiler previously had a ticket, if so what has caused the leak or failure ?

Best wishes and good luck.   Noel.

Hi Thomas I have sent you a message !  Noel.

Really, to be able to advise from here, we need know The Steam Workshop report.

For a start, did the boiler fail on test, so mechanically; or did the examiner simply reject it through lack of an initial test certificate from its builder?

If there is nothing wrong with it structurally, or only a minor leak that can be repaired, it can be certified via the club scheme as a “new” boiler. A structural repair would require a new initial shell-test anyway. You would of course have to be a full member of a model-engineering society to be able to use that scheme – besides, you’d want a track to run the engine on!