Don't know who can lick your butt and suck you off at the same time but I hear Charlotte Church...

...gives a quite righteous Rusty Trombone!  

Might be easier to find if you don't have a gender preference

Better yet- maybe you should interview by asking if they can pat their head, rub their belly, tighten their legals, keep their gag reflex relaxed, hold a rythym with their hands throat mouth and tongue meanwhile remembering to look up at you to ensure sexy eye contact.
Just kidding around  
The aforementioned act is not all that uncommon as a request.  
It is a bit unusual for first meetings maybe, but hey, any lady with good rythym and coordination between hands simultaneously and separately working while the mouth does two or three things at once is definitely well practiced and should be taken off the market asap to keep the unicorn ratios up and gold prices high thank you!  

Ive done it many times but usually only as a part of the oral play as my tempo gets more in tuned with theirs or if there is music to keep up with it helps to keep my hand hand eye contact, knees for up and down movement, mouth, jaw tension, tongue thrusting and flicking at correct softness and speeds, whilst using hands and particular fingers in tune with the rest of the overall action.

All kidding aside, not uncommon at all, simply a rhythmic tempo sort of thing from my experience I can get all requests coordinated and or timely once I have my knees comfy as thats where I do my best work.

You may want to be a bit more discerning when you book certain ladies as even if they may allow this play they may never allow this forward of a description before screening/meeting/and approving of the idea to play with you afterwards. Just ask for ass worship if anything or at least wait to get descriptive until after you're screened.

Even so, thats lucky lady who gets to partake there...enjoy!