Cycraguard does what you want, but, I’d say forget about downtube fenders entirely and just fire on a shockboard or shockblade crown mount or similiar (assuming the fork has an open bottom on its steerer). The mounting hardware is poor and really needs a cable tie or two to keep it solid for rough use (ie, I had one on my downhill bike- rough use) but they’re absolutely fantastic otherwise.
(other manufacturers are available)
Little mudguards, bender fenders and the like, are fine for what they are, I leave mine on all year for puddle splashing and summer mud but for winter they’re out of their depth. Downtube guards are basically all crap tbh, they’re very little use without some sort of fork mounted guard so why not go all in, I reckon.