Ebay is probably the easiest search.
Find the axle to crown length of the bike as supplied, then as that's a sus fork, you might want to drop 10-20mm
Check the steerer length and style for match (modern stuff tapered) and think about how much the clearance you need.
Avoid low quality from abroad.
Because you have little legal comeback, the quality can be truly shocking.
They are good if you like the looks, and I've seen them in different lengths.
I would say watch out for fakes though - it's a style that's been copied for AliExpress knock-offs, and some of those are only suitable for display purposes... if that!
Default spec seems to be 100mm Rockshox fork, suspension corrected rigid would be 445mm AC. Had the Exotic ones Joe mentioned, nice fork. White Brothers (now MRP) had the Rock Solid fork, there was a carbon Inbred fork but that may have been corrected for 80mm and not 100mm, Bontrager Switchblade also had a 26 option. Exotic 26 fork on eBay atm BIN £99 all in.
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I have an MRP 445mm Rock Solid fork in superb condition. Cost me over £300, but alas it's a bit tall for my bike. After £150 posted for it. Can send you some pics if it's of interest.
I run 425mm Rock Solid forks on two of my bikes and they are great forks.