Just a thought. I don't know what tools you have, but I agree with Mike, those small pieces can be fabricated. However, if you do that, I suggest you look at your design and make larger pieces to reduce the number of joints.
For example, rather than make/buy the 8 pieces in the 2 circles on the left in the photo, make 2 larger pieces that are 6.5" and 6.0" respectively. In fact, you could combine the 2nd set with the two 10" pieces to make just a single 26" piece out of a 40" straight. The leftover 14" could then be used to make the 6.5" piece. Rather than buy the 2-10", 5-1.75" and 3-1.25" pieces, you'd just buy 1-40" piece. Altogether you'd eliminate 8 joints and still have a ~7" piece left to use elsewhere.
It'd be the same with the 4.5", 5.5" and 10" pieces in the middle circle (though they should really be two 10" pieces to begin with).
There are also several places where tracks don't join. I think some are close enough to fit, but if not, you're going to need to do some cutting to make the design work. If you have to cut one, you might as well cut the others.