I built one when I started sailing some 12 yrs ago! It was then bought from Bell the people who built all the mirrors... if they are still building them try them. If they have stoppped then I guess Trident may have taken over.
It was very easy to do and also a great feeling... if you want to race it then you should look at some of the racing mirrors as there are many things you can adjust/change whilst building it to help with weight and comfort etc.
I built a very special one a few years ago. I handpicked all the precut solid wood pieces and ply panels in the Bells workshop. It was assembled very carefully, all wood was was epoxy coated, epoxy fillets were used instead of polyester, the copper wires were removed and it was sprayed with dark green two part polyurethene.
The quality of the ply was not very good even after selecting panels.
It was not an innexpensive boat but was very well looked after. Even then one of the ply floor panels cracked with stress. (I had deliberately not substituted any of the standard ply panels with higher quality ply to keep within the rules and the spirit of the class)
The original owner kept it for three seasons and raced it with good results (Scotish area champion for three sucessive years) It was then sold at a very high price.
That was something like twelve years ago, just before Bells closed down. I think Trident took over at that time.