There are 2 type Parker (more commmon in the NXT) which is a black solenoid with the upper already soldered in place.
Or the Humphrey style grey in colour (not found in NXT's from teh factory but is a much better solenoid) the upper board is easily removable (which is one of the reasons I like it more)
Both can't be purchased direct from Smart Parts or your chosen shop providing they have dealings with SP, it's not usual for shops to have solenoids as stock as they should be an uncommon replacement (I have 2 dead parkers here, switching to Hump's as soon as I get the £££)
Warped can get them, as can Lips, FatBobs should be able to(shop is open tomorrow)