I finally found 40W Delo 100 today at the pretty good price of $8.55/gal at Fisheries Supply in Seattle. However, to get this price you need an account there.
West Marine in Seattle, Edmonds and Anacortes carries it also at a slightly lower price but didn't have it in stock except in Anacortes, too far for me.
My son found out from one of the guys at Fisheries Supply that there is going to be a big price increase in Delo on 1 June. What else is new? He didn't know if it was Delo 100 or 400 but it is probably both. I'm hoping the increase is only for 400 since it is by far the biggest seller of the two, but it is probably not a bad idea to stock up now.