I have bought a couple of bits from Westlake and can recomend them,they are very prompt with delivery. They are on that well known auction site and are based at Peakirk just north of Peterborough.
I suggest you contact Neil Jarrett who is very knowlegable about Ransome MGs. He is on this forum and his email address is neiljarrrett at btinternet.com
Neil Jarrets email is njarrett@btinternet.com Neil will send you his current parts list. There are several magneto repair specialists listed on the VHGMC prefered suppliers list.