There was a 1/48 Collect-aire RB/B-66 available which still shows up for sale occasionally. I have a copy in the stash:
Likewise, Collect-aire also did a 1/48 B/RB-45A/C Tornado - also have copy in stash:
I also seem to recall someone was releasing a styrene copy shortly or perhaps I am mistakenly thinking of the 1/72 Valom one...
1/48 XB-70 is taken care of by HpH. you just need to decide which child or body part you are willing to sell in exchange...
There used to be a 1/48 Attic Resin P2V neptune available - they still show up occasionally:
There is also a 1/48 Vacuform version available from Combat Models:
A 1/48 B-32 Dominator would be great. Apart from one scratch build I have seen (see
here), no-one has a kit available as far as I understand.
Also, no-one has done a 1/48 B-2 at least as far as I am aware, though Combat models did do 1/48 versions of the XB-35 and YB-49.
RB/B-47 is served already by Sanger as well as a resin one that I have in my stash (no name as far as I recall).