I swear I checked mouser. I must have typed 74LS186 or something
Mouser, Digikey, Newark, etc. have some real issues with the search parameters on their websites. The 'parametric search' feature - where you lay out component parameters one-by-one, and let the site search for you, is the biggest culprit. Often, the site will give you a null result - but searching by an alternate path, or a direct phone call will show parts in stock.
There are several ways to "backdoor" their stock lists - but sometimes you have to really work at it from several angles, keep an eye on supplies, and stay on your toes. As an example - I recently had an issue with sourcing an IC we're using in production. I learned during a chance social conversation while on vacation, that there might be some upcoming issues with supply of that part, because of a possible patent dispute involving the manufacturer. By the time I was back at work the following Monday - I discovered we had only a few week's supply of the part on hand - and an online search indicated that worldwide inventory was drying up. The search showed 300 pieces at Newark, and about 1300 in the UK at Farnell - plus some lower temp commercial parts in China. By the time I could get a purchase order through the system (about a half hour), the Newark parts were no longer available - though they still appeared up on their website. Now, things were getting serious! Since Farnell / Newark is one entity, we requested to purchase all of the UK stock. "Sorry - there's a limit of 300 pieces per buy, because of some kind of supply issue". 5 phone calls, and 5 separate purchase orders later, we secured all 1300 pieces - and won't have to redesign for at least 6 months.
Sometimes, you get stuck by obsoleted parts, and have to re-design a circuit, or find alternate sources for the parts, or variations (ROHS vs lead-bearing solder, different temp range, screened parts, different mfr, alternate packaging, etc). We've been forced to make 'lifetime buys' a number of times - but sometimes, there is another source, an alternate part, or 'hidden' stock. You just have to keep digging.