Is there a headset thingy that will make this work?
Struggling to find a second hand straight steerer 650b fork for my gravel bike.
I could go Chinese but clearly I’d die in a ball of flames
What diameter is your steerer tube?
If it has a 1 1/8" internal headset, then it should have a 44 mm internal headtube. You can fit a 1.5" external lower headset bearing which will allow a tapered fork.
If it has 1 1/8" external headset with a 34 mm internal headtube, you will be out of luck.
https://www.bikeradar.com/features/the-ultimate-guide-to-headsets/
As above you need a 44mm internal headtube and then you have a choice of lower external cups from Hope, FSA, Nukeproof, Brand X
https://www.chainreactioncycles.com/nukeproof-neutron-bottom-headset-cup/rp-prod124574
You need EX44-40 - B5 On sale at the moment £9.99 Bottom cup only
https://www.chainreactioncycles.com/brand-x-semi-integrated-44iets-sealed-headset/rp-prod208221 - Top and lower cups
What bike is it?
I ran a cube frame that took a 1/18 steerer with a hope external headset. It did add about 1cm but I didn't notice. Probably proved it.
I could go Chinese but clearly I’d die in a ball of flames
Most things are Chinese in the bike world, you can't really say this anymore as there's so much variation. Brands like Trifox, winspace, ican, Farsports etc and even to an extent new brands like airwolf are all worth considering and have come a long way from just "a Chinese frame or wheel"
If you do go down this route just do your homework and ask on the forum for other uses experience and try and avoid forgeries if you can.
You can do this is you have a semi-integrated headset currently (44mm ID / ~50mm OD head tube). The external lower cup headset for a taper fork will add ~12-15mm to effective fork length so that's about 1/2 to 3/4 degree slacker overall - you may be able to get a shorter carbon fork to balance this up, 395 vs 400mm AC, that sort of difference. It's not make or break but it'd be good not to add excess cup depth or fork length. Carbon forks can be shorter than a steel fork of the same tyre clearance anyway.
Said this before somwhere. Last century I stuck some KDX200 forks on a Derbi Senda 50. The lower head bearings were way too big. I had machined a top hat shaped lump. The naoorw bit went into the frame, in your case possibly 1 1/8th and below that was a flange that took the bigger bearing. On a push bike you would only lift the front end by the thickness of the bearing. That could be compensated by shorter forks or maybe the added height would in effect slacken the angles a bit thus being more modern. Seat tube could be faked by spinning the seat post around as TT bikes sometimes do.