There is a Manta owner's group, but it doesn't list all of the boats. I have a list of all of the sailcats, but none of the powercats. I don't know how many they made, but there is someone in the group that has powercat #11, so they made at least that many of them.
I don't know what you mean by parts
- for the Volvo
or for the Manta? I suspect both are easy - the Volvo is still a current engine
and Manta used a lot of common, standard parts sourced mostly in the US.
There is a legit attempt to restart the Manta brand by one of the original people involved in the company. I wrote about it in another thread and have since learned that a design brief has been published in water
Sailing, but I don't have a subscription to that magazine. Perhaps someone here does and can post it?
I do have some drawings from the Facebook page. The naval architect is the same as for the Manta powercat, so you may see some design cue similarity.