Most of us have to make our own, they are very rare, particularly in the size you require and can often be very expensive. I would suggest getting hold of a wooden flat bottomed smoothing plane (better to have a narrow mouth). Shaping the bottom to be convex is fairly straight forward. The method I use is to first find a concave curve to match the convex curve you want on your plane. I have found old section of gas pipe are excellent for this if you can find some. The pipe is plastic and can be cut with a hand saw if you don't have a bandsaw and should have a wall thickness of about 18-20mm so it stays rigid enough. Obviously the pipe diameter should match the curve you want on your plane.
Remove the guts of the plane and roughly shape the flat bottom to a curve using a traditional flat plane. After sticking sand paper to the concave surface of your pipe with double sided tape work the curve into the plane until your happy. Next take the blade and possibly metal chip breaker if the plane has one and grind the curve to match the now shaped plane bottom. You can get a marker pen and use the bottom of the shaped plane as a template by poking it though the mouth of the plane. Once you have a reasonable ground shape on your blade you can change the sandpaper for various grades of wet and dry to hone the blade in the gas pipe former (it's a good idea to purchase a honing guide).
Good luck it takes a bit of patience with the blade but you should get a perfectly serviceable convex plane.
Cheers
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Topic: Round bottom plane (Read 5454 times)