If you look carefully - here, ebay and certain online shops still stock thread (quill) and threadless (ahead) type headsets - think it'll be 1" (but spesh experts are on here plenty
They range from a tenner up to 100 notes for a chris king. Personally i'd keep a quill stem as stumpy's / hoppers are some of my favourites of the time and just look right as they were out of the box.
Quill stems are also available - look for a syncros (possibly a bit bulky), a tioga t-bone / avenger or maybe something finer - if you're staying with canti brakes then you'd need the stem to have a carrier or a headset fitting (hang doggy or similar) to end the cable.
Rigid forks are available - plenty of project2 (kona's - come up here - you'd need to check your steerer length to suit your headtube / headset stack height / stem. You might even find someone selling an original stumpy of rockhopper pair on here or on ebay.
Flat or slightly swept alloy or chromo abrs are on here a plenty. beware modern bars and old stems as sizes are different at centre.
Like a fish ever needed a bicycle anyway...MTB: '89 MF Alu Team Pro,'88 Muddy Fox Courier,, '92 Orange Elite (now 17"!), '04 Kona Fire Mountain (now Son's), '96 Muddy Fox Ranger home-build (son's), Specialized RockHopper '92 (Ad's retro-build) ,'02 Kona Scrap Special Edition OB (3rd Son's), 1989 Orange Clockwork (Gone!?)
ROAD 2013 Orange CarbO ,2012 Basso Devil (3rd son's), Colnago CLX3.0 Di2 self-build