Like many others I have used Windex glass cleaner to strip most acrylic paints except Vallejo (I now try to stick with Tamiya). However it is expensive (£12-£15) and not readily found in shops, so in search of an alternative I have found "Stardrops Power Cleaner with Ammonia". It is £1.20 from such as "onlinepoundstore". It works much the same as Windex, seemingly due to the ammonia content, albeit more slowly.
It can be diluted and works equally well (not sure yet about gloss though) so is even cheaper. It comes with safety warnings re eyes skin etc. so care should be taken.
Hope this helps.