For one time, you could use expertflyer's five-day free trial (actually a five-day cancellation privilege, but they promote it as the same thing). You'd have to pay a few dollars to repeat the next time, but many people find it worth the money to resubscribe for a month each time they need it.

Otherwise, if your needs are only on a specific airline or alliance, there may be focused options. For example, ANA has something that works for *A flights. You need an ANA frequent flyer account to use it, and you're supposed to have miles in that account, but there are currently "back doors" to get around the second requirement.