Good day, if anyone is ever searching through the threads because they are looking for a similar item, I found and ended up buying this little guy...
http://theevolutionstore.com/store/black-rat-tx0026/ He's not a brown rat but should meet my requirements as an art study just the same.
In the meantime, if any of you taxidermy artists ever end up with a really nice brown rat specimen that you'd like to sell, be sure to send me an email because I may still be interested. Thank you for all of your assistance, I did receive a few pm's of possibilities and am grateful for the help. I'm sure I'll be on here looking for other animals in the future.