This usually happens to me when it comes time to ordering food at a restaurant. With me it’s usually along the lines of “I’ll have the ……..” and then I block and just face the menu at the waitress while I point at the item I want. However I always try to take a breath when the block happens even if it’s an awkward pause and try my best to spit it out. Another way that helps me get passed known blocks of mine are merging two sound. For instance, when I try to say “I have a mobile order for ____” at a drive-thru, i block on “I”, so I form it into “iave” and it helps a lot. So maybe try doing that? Let me know your thoughts!