Reddit mentions of MonkeyJack Trekking Butterfly Handlebar Alloy Multi-Position Handle Bar Bike Bicycle Bent Bar - 31.8mm

If you do the MTB conversion route, the easiest way to keep costs down and get hand positions is to use trekking/butterfly bars. That way you don't have to buy new brake levers and shifters. Clip-on aero-bars might also be worth considering, they are a revelation when riding into the wind and pretty comfortable if set up a bit higher than the typical triathlon setup.

Consider the choice of MTB carefully; some have really long top tubes and you might be stretched out too much for your liking. Some have all sorts of braze-ons, others won't have rack mounts. I've done a few MTB conversions and they work out alright but the trick is to find one that's in great shape and lived most its life in someone's garage so the parts aren't rusted together. Check for stainless spokes and a cassette hub, no point in dicking around with entry level stuff. There are a lot of decent 26x1.5" tires out there and they make for a quick enough ride. If you want ultimate reliability friction thumbshifters are hard to beat and are still easy enough to use on 8 speed and are cheaper than bar-end shifters for drop bars, so sticking with a flat-bar setup has advantages.

Some hybrids can also be great places to start for a touring bike, just avoid anything with a suspension fork or anything in the "comfort-cruiser" category, they're heavier and generally lower-end parts. An older "fitness hybrid" like a specialized sirrus can be a good starting point... but generally I'd look for something like a 3x8 with mtb gearing, you'll save the expense of converting the drivetrain. I did my first tour on a sirrus conversion and it was a treat, I wasn't worried about it being an aluminum frame.