I need help finding out how to purchase a Marshall Tucker Band
t-shirt, preferably an older one.  They are pretty difficult to
locate.

eBay ( http://www.ebay.com/ ) is my favorite place to find just about
everything, and they haven't let me down today. I've found two current
auctions that may be of interest to you.

MARSHALL TUCKER BAND 70's T-SHIRT IRON ON 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3532236049&category=29928

Marshall Tucker Band 79 Concert T Shirt sz L 
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2842516345&category=28022

Also, checking the older (closed) auctions, we see that they have had
shirts before.

Marshall Tucker Band T-Shirt
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3529978714&category=33006

So, even if the current auctions aren't what you are looking for, it's
quite likely that something you DO like will show up soon. You can
even set it up so that eBay will send you an email each time a new
auction you might be interested in arrives.
 
Starting from the front page ( http://www.ebay.com/ ) in the box
labeled "What are you looking for?" you can enter your search
requirements (for example: "marshall tucker band shirt") then click on
"Find It".

After doing the above search, click on the "Save This Search" link.
You can then put a check in the box under "Email Me" next to your
newly saved search. eBay will send you email each day that new items
matching your search appear.

Please let me know if I can be of any further assistance.


Search Strategy: 

(On eBay)
marshall tucker band shirt
http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&krd=1&from=R8&MfcISAPICommand=GetResult&ht=1&SortProperty=MetaEndSort&query=Marshall+Tucker+Band+Shirt