As someone with the same problem and brainstorming ways to fix it I'm going to try to help. If you're able to recognize that your opponent is get-up attacking then that's good. You've already got half of the problem solved. I'm going to compound the points made by the other posters. Generally you want to bait the get up by running up to, then tricking them to get up attack. There are a lot of options here like shield stopping, wavedash down (good way to bait things out in general), dash dance toward-back-then-toward your opponent to grab, etc. If you find yourself out of range what you can try doing is running into a shield stop. If you shield while running you'll still carrying the momentum of the run and slide forward a foot or so. You can use that to range yourself into a shield-grab into a u-throw to u-air juggle. If you opponent isn't getting wise to this and failing to adapt you can then mix it up with dash to-away-then-to then couple it with a dash-canceled u-smash if they're at death percent (x > 95%). There's a lot you can do with Fox's tools with this one option the opponent is displaying.
One thing you can try to do is shadowbox. I'll post the link here.
Try playing by yourself and imagining that in front of your Fox is any character laying on the ground. You know that your opponent will get up attack. Proceed to try out different options that you can use to punish that option. Then imagine they wise up. Once you've initiated the tech-chase imagine he tech away. He techs in place. Techs in place to shine. Misses the tech, lays down, then neutral-get-up. Try to understand what Fox can do in a single situation, then move on to the next option the opponent could choose instead.