Dave,
Someone on Ebay sells/auctions a copy of BF Franklin (US agent for Darlot)/Darlot catalogs on CD. I don't recall the time period covered, but you can find the auction easily enough. Unless you are absolutely wedded to Darlot, you might also look for Clement & Gilmer lenses. I have some and they are excellent. You might also try Camera Eccentric. He has alot of old catalogs and info online. PM me if you can't find any of this stuff. The Vade Mecum lists a 21 inch Darlot with 60-75 degree coverage (1888) but doesn't list any other useful data that I can see.
Cheers,
Richard