It is all in the patent (#6703009). In the most preferred solution,
Isopropyl Alcohol 70%
Water (Reverse Osmosis) (just use 70% alcohol from the drug store)
Propylene Glycol 10% by volume
Acetylsalicylic Acid 15% by weight
Glycerin 2% by volume
Cyclomethicone (obviously less than 2%)

However this does not match the ordering of ingredients in the product. It is more likely, Tendskin used the "more preferred" solution, possibly due to the cost of Acetylsalicylic Acid, or the problems keeping it dissolved it that high concentration:
Isopropyl Alcohol 70%
Water (Reverse Osmosis) (just use 70% alcohol from the drug store)
Propylene Glycol 10-15% by volume
Acetylsalicylic Acid 10% by weight
Glycerin 4-5% by volume
Cyclomethicone (obviously less than 4%)

by the way, this is a really high concentration of Acetylsalicylic Acid. it would take about 150 extra strength (325mg) aspirin for this concentration. Just buy it in crystalline form from http://www.sigmaaldrich.com/