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That adapter can be found at Area51Tactical and CDNN. I tried to post links but I wasn't allowed to. Do a search for Picatinny Rail Adapter or Tactical Rail Adapter.

I think the only thing you should decide on now is whether you want the traditional DA/SA (V3 models) or the LEM triggers and with/without the thumb safety. On the HK45 and HK45C, if you get a DA/SA, and later wish to convert to LEM, there is a factory LEM kit that you can buy and do yourself, or send to HK to do it. For the P30, HK doesn't have a kit and doesn't support any conversions, although a few people figured out how to do it - I wouldn't personally. My collection of HKs is mixed, with two being LEM and two being TDA, so I've been lucky enough to take my time deciding which I like better. I'm leaning towards the LEM for the consistent trigger pull. Note that the LEMs are more difficult to find though, since they seem to be more in demand and I've noticed less LEMs on the market vs the V3 models.

Have you measured the opening of the barrel chamber? I had an M&P9C that had stuck cases that needed huge amounts of force to unlock the slide. Sending the gun into S&W, they returned it after polishing the barrel and I continued to have problems and sent it back again. This time they gave me a new barrel and I haven't had that problem since. The same exact problem occured to me with a Kel-Tec pistol and learning from the previous incident, I measured the chamber opening and found it to be smaller in diameter than the max outside diameter of the 9mm per the spec. It took the company two tries to find me a barrel that had the chamber sized correctly. Since then, it's run smooth.

Mike, you're talking about two different guns. The P30 comes in 9mm and .40S&W only. If you're looking at HK's .45ACP's, then you have the USP, HK45, and HK45C (compact). I have a P30 (9mm) and HK45C. The P30 has the spiderman grips. You probably saw the HK45 that has similar grips but is larger overall (including the grip size). The USP and HK45C had different grips that are more flattened. In my opinion, the .45 shoots as soft as the 9 and I think it's because they both feel "right" in the hand. The HK .45s have a lower magazine capacity, and that's because they kept the grips slimmer for those who don't have monster sized hands. I kept passing up the massive grip frames of the Glocks, FNH, and Sigs until I found this one. I don't think you'll be disappointed with either.