LV used to sell a long handle scraper, and WB sells one today. The LV one was great, about 14 inches long, cast iron, cheap. Probably Kuntz. But all it was was a long thing with a 2 inch square scraper blade about 1/8 inch thick. The ones I see for sale now have three surfaces which is one more than on my square model. But they looks like they might bite one if one got careless.

A useful tool that got a lot of plaudits when it was first introduced was those vibratory saws/scrapers. They will do things nothing else will get at. Might be the best for getting into corners. I own one that cost about 40 bucks, but the one that got the high recommendations was the original fein oscilating saw, for it's ability to get into corners and coves. I sometimes use my cheapo with the saw blade to act as a precision scraper.

In desperation one tries a bit of everything. I will use a chisel, surform, micro plane, and cheapest of all a hacksaw blade. This article shows how the Gougeons came up with a hacksaw fairing tool that they sandwich in wood. I just grab some dollar store blades and hold them in my hands. You can bend them and get a loop into tight corners.