Welcome to the forum gritaHeard, yes we post-op lovers are in the minority, but there are a few of us!
In Bangkok Straps Bar in Nana Plaza is 100% postop lbs and have some of the most beautiful ones on staff. However they deny having lbs on staff and claim they are all gg's. Definitely not true! The biggest drawback to this bar is the mercenary pricing - they will ask for the bar fine and fee for the lb up front and usually a higher rate than any other bar in NEP. It seems they get enough business to continue this bad practice. Paying all up front generally means higher odds of a lack luster encounter from the lb. Some of the other bars in NEP have a few postops. If a gogo bar doesn't have a 100% all ladies sign on it, there are good odds that a few postops are there - again they will deny it if you ask.
In Patpong the venerable King's Corner still has a few postop lbs, however they are shifting to an all gg mix, and sadly this former number one bar for postops has faded badly. They used to be around 60% postop lbs and 40% ggs, and now it is 70% ggs and 30% lbs and dropping. There is another bar just across and down the short connecting passage as you exit and turn left from King's Corner. It is called King's Corner 2, but in actual fact is the former King's Castle 3, which has shifted location - it's former spot has now been turned into King's Massage Parlor. King's Corner 2 has a mix of preop and postop lbs. Some of them are quite lovely, especially on weekends, when the part time staff work (university lbs).
As far as Pattaya goes, there are no dedicated postop bars there that I know about. There are probably a few scattered about working in the gg bars, but they are keeping under the radar. There may be some freelancers working on Walking Street down around the Simon Bar Complex.
Unfortunately with the total renovation of Soi Bangla and loss of Soi Tiger where C&D's use to be, the scene there has been scattered and we haven't had much news about the situation there.
You could also try the cabaret shows in each of the cities. You will likely find some postops working there - however the approach has to be different as not all of them may be in p4p. After each show there is a photo session where they can earn some extra money from photo tips, posing with the tourists. If you are interested in one, chat her up - discretely inquire if she is postop, and then slip her a piece of paper with your mobile number on it along with the photo tip. If she is interested to meet you, she will give you a call.
You can use Thai Friendly as well, but there are very few postop lbs advertising there.