If your local hobby store doesn't carry Thunder Tiger engines, then a few of the better online sources are:
http://www.thundertiger4u.com
http://www.infinitehobbies.com
http://www.ehobbies.com
http://www.paulsmodelsupply.com
http://www.radicalrc.com
I've purchased Thunder Tiger products from all of the companies above except Radical RC, and I've been happy with the service from all of them. I'm sure I'll buy from Radical RC someday, too. Infinite Hobbies ships orders over $100 for free, while thundertiger4u.com ships orders over $150 for free. Any four stroke engine order should qualify for free shipping from either reseller. While who has the best price on which particular engine may vary from time to time, Thunder Tiger four strokes generally price out as follows:
TT F-54s - $169.99 to $179.99
TT F-75s - $169.99
TT F-91s - $184.99 to $194.99
The model number for the F-130s will be TTR9805. While it was shown at the iHobby Expo, no official pricing or release date has been set yet.
Thunder Tiger four strokes are sometimes criticized for being heavy, but only the F-91s is heavy in comparison to similar competitors. The F-54s and F-75s are actually about as lightweight as Saitos of similar displacement.
The F-91s weighs in at a whopping 25.7 ounces w/ muffler while the O.S. Max .91FS II Surpass weighs in at 24.2 ounces with muffler, the Magnum XL .91 RFS weighs 22.4 ounces, and the Saito .91 weighs 19.6 ounces plus muffler (around 21 ounces or so with muffler). Considering the lightest engine in this same displacement category is only about four ounces lighter, the F-91s isn't that much heavier than the competition. It's often a good choice for scale projects or planes with long tail moments like the Goldberg Tiger .60 that benefit from a little extra noseweight when it comes time to balance the CG.
Ace Hobby provides all warranty service for Thunder Tiger engines here in North America. Thunder Tiger parts and service are provided worldwide and all Thunder Tiger engines come with a 3-year parts & labor warranty.