You can get research chemical (RC) benzos legally, but it takes some effort.
There are probably dozens of RC benzos, a couple of common ones are bromazepam and flubromazepam.
Even though they're legal, it's still difficult to find legit sources. To start you can search Google with something like "buy bromazepam". You'll get a ton of junk but mixed in will be shops claiming to sell the stuff. Make sure it's not from the Netherlands because they won't ship to the US. You also need to make sure they're not claiming to sell things like Adderall, Fentanyl, or LSD which is obviously a scam (there are a ton of them).
After finding a supplier you have to decide which benzo to buy. The ones I listed above were both listed in PPH as benzodiazepine substitutes. You can find information about the others on the internet. There's also info on Reddit in the r/rcbenzos4 subreddit.