There are a zillion companies/websites out there that can provide you consulting and acquisition services. Many are very reputable... many are not customer oriented. Buyer beware.
As an investment banker, I'm sure you are able to research options and understand costs involved with maintenance and operation. I've read a few articles about Austin Jet, and they seem to be a customer-focused company. I don't have any first-hand experience, but Austin Jet is one of the most successful in the business and represents the BUYER (this extracted from independant news articles). He seems to have good success with fitting the right aircraft to the right person at the right price...
http://www.austinjet.com/
I've talked to the folks below, but never went as far as an actual purchase...
http://www.northernhelicopterconsultants.com/
I've also heard decent things about Mike Green & Associates. However, they are based out of Tyler, Texas (the most racist city in America - as reported many times in various newspaper and TV specials). Hopefully, his location isn't a reflection of his ethics...
http://www.greenheli.com/index.html
Finally, the following two sites (there are many others) can give you valuable comparative data. I probably wouldn't use either as a primary means of acquisition, but you might find a good deal from time to time...
http://listings.ebaymotors.com/aw/pl...428/index.html
http://www.rotorworld.com/heli/