Not sure why you were waiting for an e-mail from
www.thundertiger4u.com, the crankcase for the GP-61 is right on their website. Search for PN0065 and you'll get a price of $25.21.
The folks at
www.infinitehobbies.com list the same part for $27.39.
Even
www.eHobbies.com showed the GP-61 crank case as available for $27.29.
Lots of good Thunder Tiger resellers out there with pricing available simply by punching the part number in and clicking on "search." Why does everyone say Thunder Tiger parts are so hard to come by?
Edit: I thought $25.21 for a .60-size crank case seemed pretty reasonable, so I pulled up some comparable engine parts for fun:
$49.99 Natural crankcase for O.S. Max .65 LA
$40.99 crankcase for Super Tigre G-61/G-61 ABC
$29.99 crankcase for Tower Hobbies .61
$49.00 crankcase for Magnum XLS .61A
$18.95 cranksase for Evolution .61 NT (wow!)
Apparently Thunder Tiger parts are not only readily available, but they're cheaper than most of the other major brands.