I had a threesome last month, two 'girls' from Voodoo (ground floor, back left, Nana Plaza). The second one, post-op LB was under training ("She [of the first, definately female] teaching me, she
professional") and had a not too well fitted boob job, so may not qualify for your defination of a LB..? The two worked together well and were pretty business-like, ST as it turned out, but it was good fun for a one-off.
Anyways, NEP is the place to start your hunt. Try Voodoo, or Temptations (2nd floor South (near escalator) or the other bar which seems to be 'half and half' in the SE corner of the 2nd floor (I don't mean the usual LB bars in the NE corner - I don't know if they have any 'real' ladies working alongside the LBs.). Talk to the mamasan, she'll hook you up (if 'she' doesn't join in herself
) You could try the FLs outside NEP, but it's unlikely you'll find the pairing you seek and that they will work well together and be relaxed with each other and with you.