I am reliably informed that MTP clothing is not 'officially' illegal to own as soldiers are at liberty to do what they like with stuff written off their form blah, blah, blah.
The disposal contractor apparently has "TONS & TONS" of MTP of all types in stock but cannot sell it on until June of this year. Then we'll see what variety of kit is out there.
Kevlar and ceramic insert and ballistic helmets are not disposed of - at least not yet - but the odd used one isn't thought to be an issue. New ones should not be available and the SIB would look actively into how it got where it got. There are a few squaddies who watch ebay and inform the authorities of things they feel shouldn't be out there. How often this gets taken up by said authorities is anyone's guess. The main concern isn't the odd guy selling something but serious crime from QM and in bulk.
I have a number of things from UKSF mates. Nothing illegal but they have a freer hand to use and dispose of things than the average squaddy. Those things are usually given to me on the understanding i do not re-sell for several years and with no names readable. I never refuse - it would be rude
Nor do i tell anyone what i have. Some things i collect and enjoy sharing, others i keep to myself. An SF helmet would come into the latter category.