Lestat,
A few notes -- but
not for clip-on mudguards, however. Are clip-ons what you
must have? I ask, because I used to run some on my 700c derailleur bike, and their coverage was very limited.
With that proviso --
1) I have a Raven, currently fitted with Schwalbe Supremes, 26 x 1.6 (actual inflated: a hair less than 40 mm.) I use 650B x 52mm Velo Orange Zeppelin fluted alloy mudguards. With spacers to bring the clearance to 15 - 20 mm, the 650B size works very nicely indeed.
I have also fitted a front mudflap from Dutch Bike Bits, here:
https://www.dutchbikebits.com/mudguards-chainguards-fenders-coatprotectors/mud-flaps/bibia-touring-mudflap Yesterday, I rode in a cold rain for four hours, half of it into a stiff north-westerly. Messin' about in such (Scottish) weather isn't my usual or preferred Thing To Do, but this was a charity ride for the Children's Hospital of Eastern Ontario; the Bibia worked very well.
2) I just bought a pair of Maxxis Overdrive Elite 26 x 1.75 touring tires from Chain Reaction Cycles, on clearance for CDN $ 65 each. They are
said to be 42 mm inflated; if so, they'll fit nicely with the 650B alloy mudguards now on the bike.
3) Another option I'm going to look at is a pair of 60mm VO alloy mudguards, also available in stainless steel, here:
http://store.velo-orange.com/index.php/accessories/fenders/26/vo-60mm-polished-fenders-26.html Those will fit the 26 x 1.75s very well, and would work for 26 x 2.00 Supremes, or for a pair of Compass 26 x 1.8 tires that I'm considering as well.
4) Lastly, I've just seen that Planet Bike now offers a 26 x 60mm mudguard, the ALX 26 Wide, made of alloy & available in black or silver. Here:
http://ecom1.planetbike.com/ALX26Wide.html Price is around USD 65/pr, I believe--for some reason, that link does not show the price.
Not sure how widely available Planet Bike products are in the UK--or Velo Orange, for that matter. I know that SKS have chromoplast mudguards in the 55m size, well suited to 1.75 tires, but the VO items are longer, and hence give very good coverage.
Hope that's helpful -- good luck.
John