Bike parts you hate.

I had, yes, but found them difficult to find and even more difficult to get them at an acceptable price. I was never sure what to search for (is 'ISP topper' the only/main name they're known by?). Any cheap versions / good places to get them?

Have you considered a bigger top to your ISP? That would let you use a normal ISP topper. Ritchey is in 3 sizes up to 38.35mm, which is presumably big enough that you could wrap your bamboo with some crabon fribé to build it up to the required diameter and roundness