I'm no expert on this but live fairly close to the Speyside and eastern highland group of distilleries in NE Scotland. I don't know of any specific tours from the USA to Scottish distilleries but feel sure there must be some. If you wanted to put together your own package I'd be happy to give you what advice I can. Here are some things to consider ...
By booking enough in advance you can get quite cheap internal flights from London up to Aberdeen or Inverness (see easyjet.com or flybe.com), or better still, fly to Glasgow and start your tour from there. Hire a car and do a trip up the west coast then over to Inverness / Speyside, back down thro Perthshire and back to Glasgow. Depends how many distilleries you want to take in and the problem would be that unless you have company it will be difficult to drink the samples you get then drive! Public transport would not really be practical.
Better idea ... There is a Speyside Whisky festival twice a year. See http://www.spiritofspeyside.com/
. Base yourself in Dufftown (50 miles from Inverness or Aberdeen airport) and choose which events / tours you want to do. Transport is provided to most I think, and there is a chance to see round distilleries that are not usually open to the public. Best thing is the 'Whisky Fair' that they put on ... don't expect to be sober when you walk out! There is some good B&B accommodation in Dufftown but you would need to book a long way ahead I suspect. I use 'trip advisor' to find good b&b accommodation - expect to pay £35-£40 per night.
Alternatively The Glenlivet offer a 'Whisky School' lasting 2 days and 2 nights with full board. You just need to get to Aberdeen then take a taxi or hire a car for 3 days. I went on it a couple of years ago with a couple of mates and it was fantastic. Exceptional value. (£250 at that time).
The west coast island distilleries are a bit harder to get to but worth going to one or two just to see their settings and the landscape. All depends on how much time you have and what your budget is.
Hope this is of some help and encourages you to make the trip!
All the best.