And of course I sold all my PLM with the on-center mounts I ended up buying some new ones recently but I was sad to see the on center mounts were discontinued
Personally I'm in complete disarray at the discontinuation of the entire silver PLM lineup bar the 64inch soft silver. I think that deep silver umbrellas are a nonsensical idea for various reasons (most of them related to the fact that most causal relationships and characteristics attributed to them are just factually completely false, such as that deeper = more parabolic = more control) and that only Paul Buff had both the right concept and a decent execution regarding silver umbrellas.
If we are loud enough, Paul Buff may re-introduce the soft silver in other sizes, so please don't hesitate to ask them via mail or social medias. Personally I'd like to see the 51" reintroduced (it's my most often used modifier) but I guess most people are asking for the 86". I believe that there are no plans to re-introduce the extreme silver.
The soft silver doesn't require a perfectly centred source to function properly, and I believe that Paul Buff sells a specialised umbrella reflector which may be a good solution for you (I'm not sure, I don't have PCB lights and modifiers).