i think it is easier to find a petri 40 than a 38. but you are correct, the correct hub, hub cover and horn button is the tough part. and to my knowledge, they were never sold separately. a leather CSL 38 petri with the long hub + cover is the rarest beast, and that in great shape is north of 2000 gbp ,,, IF you can find somebody willing to part with one. i have heard a rumor of a great 40cm in germany that might come up for sale later this spring ... otherwise you should keep an eye out on ebay.de. pay attention to the quality of the metal and avoid oxidized metal spokes.