There were a number of backyard builders manufacturing copycat Hagons in the sixties. Some were pretty nice, others were dangerous crap. I had an Aussie made Taylor frame that was very similar to a Hagon Sand Tracker and the welding and little details were actually better than the Hagon original. Jonesy's got a couple of Aussie made speedway frames that look pretty neat as well. Of course, because 4130 and Reynolds tubing was hard to find, they were all made from seamless mild steel, but so are most UK speedway and grass track frames come to think of it.
There was a mob called P&R that made nice TZ frames (among other stuff) back in the 80's. I have a vague memory of seeing a custom framed YZ125 at an Amaroo Park MX in the early 80's and recall thinking how trick it was. I'm almost certain it was a P&R frame. I can also recall a bloke in my club, Annandale-Leichardt that worked for Qantas who built a sweet Maico-ish chro-mo frame to suit his Yamaha SC500 engine in about 1975. He'd gone to the US and brought back Arnaco shocks and cool translucent plastic 'guards and a B50 BSA style tank that we'd yet to see here. I went overseas myself not long after and when I returned 6 years later the bike and its builder had left the club, and presumably the sport. It was a beautiful thing, all TIG welded using Maico forks and a rectangular tubing swingarm with 45 degree laydown shocks. A photo of the bike appeared in Revs or AMCN at the time.