I have been using scrapebox to find expired tumblr blogs. The problem I am running into is that the vanity name checker for scrapebox is very unreliable you can site their and go through url after url and not find one they say is available to work . What I need is something that can accept a load of expired blog urls and go to tumblr and find out if the expired username can actually be reregisterd.
Since your original question is "Can this be done", the answer is "yes, it can surely be done". The easiest method is probably to create some basic PHP/curl script to automate this task.
Just a suggestion: if you tell how much you are ready to pay for this script, I'm sure you will get more offers.