To get used to it? Spar. A lot. Keep going when it hurts, build some mental toughness (stop if you're injured though, of course - I used to ignore injuries all the time and now my body is fucked). My old MT coach used to get us to lie on the floor, and then he'd do medicine ball slams onto our midsections and you kind of use your abdominals to absorb the blow a bit, that's another good one. Holding kick shields for people doing big leg kicks can help you start getting used to taking impact into your thighs if you're not used to it. Defense-only sparring rounds (ie. you don't strike back at all, the other guy unloads on you and your aim is just to maintain some good solid defense and evasion - works well if you also do a lot of fighting off the back foot in your gym)...
And sparring. Tons of fucking sparring. Mix in at least a few hard rounds every class, alongside lighter rounds. The gym I used to train at sparred fucking hard all the time, people who visited from other gyms always used to tell us they'd never spar that hard at their gym. Just the way our coach was. Built a lot of mental toughness. I fought with broken ribs in the ring and still kept going purely because of the mental toughness he'd instilled in us. It hurt like FUCK taking a shot to the busted ones, but I wasn't going to go out like that - you know what I mean? Went the distance. All my losses were on points, never been KOed or TKOed; dropped a few guys myself though.
Well, I'll tell you what. It was a fucking hell of a lot to put my body through for a shitty amateur MT fight, I kept training with my ribs like that after the fight for a few months and the bone never knit properly, eventually ended up having to take time off of training on doctor's orders and now have a permanent weak spot. And a lot of the other shit I put my body through, too, still gives me grief - I haven't fought MT in over ten years and the injuries I got back then still bother me. I'm stiff, and ground down, and aged probably a little more than I ought to be. And for what? A bunch of amateur fights, no gold and no glory? Aye but it was worth it to me to do something I truly loved doing.
Reason I'm telling you this second part is just for you to consider a little bit, whether or not the toll you'll be taking on your body is worth it to you. If it is, then try the stuff I mentioned. If not, maybe consider finding more constructive ways to build that mental toughness without grinding your body down, and use that mental toughness when you compete.
My .02
