Grob yes you can make them at home, but you'll need a little practice.

1. Scribe a circle on some 25mm ply (your tube will spring a little so go 10-15mm small than the required inner diam.

2. create a clamp and bending lever as shown.

3. clamp in some suitable tube (20 or 25mm).

4. Rotate lever in one single slow movement, going beyond 180 degrees..

4. and repeat for 4 similar parts then cut to length and join with either welds or rivets..