I've been looking and can't find them anywhere. They are legal to sell aren't they?
AAC, I hope you don't mind the quote from your Evo9 FAQ:AAC FAQ
What is the A.S.A.P. System?
A.S.A.P. stands for Assured Semi Automatic Performance. The A.S.A.P. System is a product improved Nielsen device used in the Evolution Series silencers that allows Browning style host firearms (Glocks, Sigs, H&K USP's, etc.) to cycle reliably. The A.S.A.P. System is comprised of a precision-machined piston, piston bore, spring, and rear cap. It enables traditionally recalcitrant Browning inspired handgun designs to cycle reliably by temporarily relieving the pistol of the weight-burden of the silencer. Upon firing, high-pressure gases enter the silencer and propel it forward against the tension of the A.S.A.P System spring. While the majority of the silencers weight is in this "floating" condition, the host weapon's firing cycle is able to proceed unhampered. The spring within the A.S.A.P System returns the silencer to its unfired state, ready for subsequent shots. This sequence of events takes place so rapidly, the shooter is unaware it has occurred.
The Nielsen devices used by a number of manufacturers are separate modules attached to an existing muzzle silencer. The Recoil Regulator sold by AWC Systems Technology for their Abraxxas and the L.I.D. used by Gemtech for their Trinity are examples of accessory module Nielsen devices. Whereas this ads a level of convenience to the end user, it is a compromise because most silencers equipped with an accessory module Nielsen device lose sound suppression efficiency when compared to the same silencer without a Nielsen device attached. The A.S.A.P. System used in the Evolution Series is fully integrated into the design. This integration enables the Evolution Series to deliver uncompromising, world-class sound suppression in a compact, lightweight envelope.