As others have said, no, it's impossible. The ejaculate that women and FtM transmen can release is a clear liquid that doesn't have any sperm in it. Therefore no pregnancy is possible.
I'm not sure what you mean when you say "post-op FtM's" . . . there are several different FtM procedures, from a metoidioplasty to a phalloplasty. There are still some scientists who think that not all women can ejaculate, so if an FtM couldn't ejaculate when they were female, they probably won't be able to do so as FtM's. Hormones might also inhibit the ability to ejaculate (since they do tend to cause general vaginal dryness), but then again, I've heard from several FtM guys on testosterone who haven't lost the ability to ejaculate. And if you want to see a GREAT pornographic (pre-op) FtM ejaculation scene, see Billy Jack Gunn and Paul Gunn's scene on Crashpadseries.com. He has a literal gushing fountain- very, very hot.
I don't know of any other FtM squirting scenes in porn, pre-op or post-op. And there are no post-op guys in porn that I know of, unfortunately. If it was done correctly, a post-op FtM could technically ejaculate, so long as his urethra was lengthened to follow through the new phallus, and then the ejaculate (coming out of the urethra and paraurethral ducts) would come out of the new penis. I have no firsthand or even secondhand accounts of such, however.
I would like to address Kyle D's comment, though- there's a surprising amount of FtM porn nowadays, very easily gotten!
You can see FtM's (with either men, women, or other FtM's) on:
1) Buck Angel- he has a website, Transexual-man.com, and has many DVD's, of him with both men, women, FtM's, and MtF's.
2) Trannywood Pictures is probably the most famous company, making hot porn of FtM's with other FtM's or bio men. You can buy their films at lots of good websites or download it VOD, linked from their website Trannywoodpictures.com.
3) Morty Diamond's films- he has "Trannyf*gs", of FtM's with other FtM's and bio men, and "Trans Entities", about two transmasculine individuals who aren't on hormones. They are both available to order on his website Mortydiamond.com or for direct VOD downloads from Hotmoviesforher.com, and the latter is sold at many websites.
4) You can now buy the French movie "Pour Une Nuit" ("One Night Stand") from Fatalemedia.com. Very hot, featuring none other than the famous FtM photographer Kael T. Block, and another FtM guy as well, both with women.
5) "Full Load: Scenes From Ssspread.com" features an FtM with his girlfriend in the last scene. Can be bought from various website retailers or downloaded VOD from Hotmoviesforher.com.
6) "Pornograflics" features a very very hot FtM guy with his girlfriend. Mostly downloadable from various VOD sites.
7) Crashpadseries.com and Pink and White Productions' films often feature transmen, with either guys, girls, or transfolk.
The only FtM porn difficult to find today would be Christopher Lee's early movies "Alley Of The Tranny Boys" or "Sex Flesh In Blood".