I'd like to go with the classic '80s/'90s look for my SP5. I've got a clipped and pinned lower with full auto markings, and an A3 F stock and a drum rear sight but I'd love the flashlight fore end to round it out.

I'd like it with the shorter light, however, I'd prefer it not say "SUREFIRE" on the side like this one:

https://hkparts.net/product/surefire-model-328lmf-hk-lighted-forearm-p17632.htm

Where can I find one, or do they all have the logo?

I'm guessing that suppressors are a no-go once you have one of those forearms as well?

Anything from Surefire will have the name on it.
As for the suppressed, they used to make a offset adapter to put the light farther down. This article from last year talks about surpressing a MP5 with a light on it.

I've read that gov contract lights will not have the logo.  Most of the older ones, and MP5 parts kits you see do not have the SF logo.

Surfire sells the short LED tube/head so you could buy a surplus light and then swap out heads.  You may want to verify compatibility, but I think the article linked above shows old light bodies with new heads.

I honestly for the life of me don't understand why they haven't made a version that's sits a bit lower so it can clear a can. And not that butt ugly offset ring that you can't even get anymore. It just doesn't make any sense. It would only have to go down, what? 1/2"? 3/4" maybe?