Hey there,
well, after doing a bit of research on this site, I found some more info - but I'm just relaying, unfortunatelty nothing from my own experience...yet :-)
Apparently there's a kamer girl - goes by the name of Jennifer, you can find her in The Device at the top right of this page - who takes couples and judging from the report she did a nice job on both. Carla - also in The Device - seems to be taking couples as well, but she's not as enthusiastic as some of the others - especially with the ladies (what's up with that, I mean either you do or you don't...)
Then on page four or five of the message board or somewhere around there, I found a report from a couple who went to Park 118 and seemed to have had a good time, but there're also a bunch of reports that the pickings were slim and the hostess extremely grumpy - well' that's a turn off, especially for a first timer... I know I would lose a good percentage of my erotic eagerness that way.
There's also an escort service which offers three ladies who are available for threesomes (well, ain't that cute?) - here's the link - price is a little steep, but then again I'd rather pay alittle bit more and take my time...
http://www.erozescort.nl/three.html I believe the price for an hour is EUR 220
Anyway, I really hope you guys will find what you're looking for and I would love to hear from you after you get back.
Cheers,
MorganLeFaye