is it acceptable to walk into a real estate office and ask for properties that have been on the market for a long period of time, but haven't had any luck?? How do I go about this?

You dont do this, you will most likely upset the agents and brokers.  Also understand that these agents have exclusive agreements with their sellers that have a carry over clause. 

Not a good idea.

No. However, there might be an opportunity to work with an agent to put offers on properties that have languished on the MLS due to lack of photos, poor listing agent marketing, etc. Though rare, opportunities for wholesaling can exist on MLS properties if you negotiate right and make the contract assignable. However, please be prepared to find a way to close on the property no matter what, even if an end buyer is not found on time. Otherwise, you will have upset sellers and agents on your hands.

A better tool for expired listings or laggards may be lease options, @Taylor West .  You will need to have enough in it to give the agent some sugar, but then you could assign your option.  If you are 'wholesaling' because you have no money, start brewing your own coffee, brown bagging lunches, avoid car payments and work more!  Drive your beater to your next investment!

Thanks all!!!  I eventually walked into the office and met with a realtor who knew what about wholesaling and put me on an almost daily e-mail listing update, to include with specific types of houses I was interested in.  I do, however, realize now that it may have not been a good idea after reading all of the comments and I just was lucky to find one who was willing to help.  He also mentioned he has done and is willing to write purchase agreements too.  This also came about after I had a meeting with a title company across the street.  Thanks again.  I will not do that again.