I don't know of many companies making them anymore. But if you are still looking for a solution you should consider some shape pads and compression net or cotton pants to hold them. Molicare and seni both make these products and they can be found on Amazon at far prices in all levels of absorbency. They are very similar to the old belted style guards you are referring too. Most of these shape pads are not plastic back but they do have great leak guards and are just a diaper minus the wings to fasten them. You can always get a good pair of plastic pants to wear over them if you need that extra protection. Then of course anyone having bladder or bowel leakage at night should invest in some good reusable cloth bed pads. They are more comfortable and they do not bunch up under you if you toss and turn as easy.
Best of luck I hope it helps.
The pad and pant system that Jenny referred to might be an option. XP Medical still sells them in the Seni and Abena brands. Here is a link to that page on their site: https://www.xpmedical.com/pads/2-piece-pad-systems
The pads are basically the same size and shape as the padded area in a diaper (brief) but with no side wings or tape tabs. They actually work very well.
VERY FEW places sell pads with belts anymore. When my mom was looking for those when she was having some issues, there was only one place we found them and it was a medical wholesaler. I don't remember the company now.
I hope this helps!
An option to throw away pads are washable pads. I recently purchased some off Etsy and am waiting for them to arrive. At night I intend to wear them with incontinence underwear for extra protection.