Hi Gary,
As with all vintage bikes the VMCC Library is your first port of call for information. You need copies of the relevant catalogue, owners handbook, spare parts list and so on. Unlike some clubs the VMCC give non-members full access to their Library. You need this info to point you in the right direction otherwise you're just running around in the dark. Start there NOW, because until you have this info you don't really know what you've got.
As you say it is 172cc I presume it is a Villiers engine. Villiers made three 172cc engines in 1929. The Sport, Super Sport and Brooklands. You need to identify which one from the engine number. I would also expect it to have an Albion gearbox. Again, you have to identify which one. Again, identity numbers are important.
As far as spare parts are concerned there is no great drama. There are none to speak of so you make them. There is little about a late vintage lightweight bike that needs more than a mildly competent home workshop with lathe. Your local model engineering club is far more important to you than your local motor bike shop. They have the necessary skills. For example, making front fork links and spindles uses exactly the same skills as making a model locomotive.
Tell us more and put up photos.
Cheers,
