Where are some of the best places to get good leather straps that come in 21mm or 19mm lug widths? You can send me PM if you prefer Also what are your thoughts on "upsizing"? i.e. fitting a 22mm strap onto a 21mm lug and/or 20mm strap onto a 19mm lug. Will it cram into a smaller lug width or that isn't a good thing. I don't really like the space that is left behind when say 20mm strap is fitted onto a 21mm lug width
Depends on the watch. There are a lot of custom strap makers out there that can easily do 19 or 21. Or there are cheap ones on Amazon/eBay. High end strap makers also offer 19/21. I've got 1 of each lol. The straps are out there just take a bit more looking.
If you want "off-the-rack," check out the Watch Boys (http://www.thewatchboys.com/iwc®-style-watch-straps-c-5.html) and watchbandcenter (http://www.watch-band-center.com/watchstrap-h425-Uneven-Lug-Width.html) For custom, I've had good experience with Peter at Watchacc (https://www.facebook.com/Watchacc-Watch-Accessories-Page-202634479808387/) and with Greg Spitz (https://www.pinterest.com/922Leather/922leathercom/); check out this thread for some pictures of a 19mm custom Horween strap I got from Greg: https://omegaforums.net/threads/new-custom-strap-for-my-speedmaster-racing.35899/
If you've got a funky racing-style watch from the '60s or '70s, try Giuliano who will make a strap to order and get it to you in a couple weeks. For others, try a Heuerville strap which will take a bit longer but totally worth the wait.
uvalaw2005 and abroad520 thank you for your links/suggestions foo2rama - I am looking for some high end ones for my Seamaster 300MC Spectre (21mm) and a FOIS (19mm)
I just bought a nice custom strap from Bas and Lokes for my SM300. They offer a 21mm size on every strap they make. Sent from my SCH-I545 using Tapatalk
I have Montblanc watches that need 19mm x 17mm straps. These are hard to find, though there are companies that will custom make bands to your specifications, as noted above. I've found two ebay sellers, both in Taiwan, watch4class and powerboxwatch, that sell bands in that size.
You can find made-to-order bands on etsy. While many of the straps aren't much more than a strip of leather with a buckle, and while some straps have flimsy buckles, there are nicer ones to be found. These are casual bands, though, and not dress ones. Here's one store to get people started: https://www.etsy.com/shop/JackFosterLeather (note: I've never ordered a strap from him, but I've seen him recommended by more than one person.) Also, he seems to have an outside-etsy website where the prices are slightly less, but the default ordering process doesn't have a 21mm option; you'll have to contact him for that.
Search for 3/4" straps on eBay. You can often find some stunning NOS pieces... that's the 19mm size. Tom
A leather strap that is 1mm oversized will almost always fit, and will usually look really good. Having owned a JLC MCC2, a Rolex EXP II, and a Doxa 600T-Graph all with 21mm lugs, I'm very familiar with the scarcity of 21mm straps and I often used 22mm straps with good success. Another vote for Peter @ watchacc if you want a custom 19 or 21. Here are pics of 22mm straps on 21mm lugs.