There are alternatives to Benzodiazepines. I'm going to list some things. However, they really are not analogous to your whole Heroin -> Kratom comparison. If you are talking about a person with a Benzodiazepine dependency who experiences withdrawal without them, then that is a difficult problem to solve with the same kind of "ease" of obtaining Kratom/Mitragynine stuff.
Alcohol is obvious. It is not going to substitute 100% like a glove for a person experiencing Benzodiazepine withdrawal, but it will come pretty close. The issue is you have o deal with all of the side effects that come with Alcohol consumption which is a btich if you need to drink a lot to stay straight and you're not used to it/don't have a stomach for it in the first place.
Other GABAergic substances would be your GHB family Gamma-Hydroxybutyrate, 1,4 Butanediol and Gammabutyrolactone (GBL). These are all reasonable substitutes for Benzodiazepine dependence. I doubt anyone would complain much. These are not "easy" to acquire however, so it's not a great addition to this argument.
Gabapentinoids - I know I'm getting far away from the original question. Gabapentin is so ubiquitous at this stage that I have found it being sold in every area I have been to or lived in in the United States. Pregabalin (Lyrica) will have a very similar effect, just more potent. I would say Gabapentin is much easier to acquire in my experience than Benzodiazepines, which I find are really not that common. I'm not out there buying these things, but I talk to people every day and like to stay current.
Gabapentin is not fully-cross tolerant with Benzodiazepines. It is not going to completely relieve a person's withdrawal. Sadly, I only have others' experiences to go off of as I have never used Gabapentin to relieve sedative/hypnotic withdrawal. I have heard people say it helps immensely, but feels as if he itch isn't fully scratched and there is still a sensation of nervous tension even if it is mild. Still, for a person experiencing Benzo withdrawal, who would say no to a significant reduction in symptoms.
If you are not in severe withdrawal or maybe you are almost done with your withdrawal and looking to stay relaxed and not return to Benzodiazepines, there are options.
Kava - I advise everyone with a sedative/hypnotic issue looking for something to take the place of Alcohol to at least give Kava a try. It is not going to take the place of a double shot of Vodka, but its effects are significant. I was an Alcoholic and a Heroin addict, so I'm not some lightweight and I really enjoy Kava.
Mg Glycinate - Helps a lot with the tension in the body that comes from the absence of Benzodiazepines
Magnolia Bark - This is a GABAergic substance. It contains compounds that interact with these receptors in ways similar to Benzodiazepines. Very relaxing and for someone who knows what Benzodiazepines feel like, it is like 25% of that feeling, which is significant for a supplement
Saffron - This substance also contains compounds that work upon the GABA receptors. Saffron is more of a "chronic usage" than the Mag Bark but both can be used chronically
L-Theanine - Amino acid that can help with relaxation, pretty mild.
Some options.
Addendum: I'm sure most people are already familiar. I always bring up Clonidine when people ask about Benzodiazepine alternatives. Again, it's not bought at the corner store, I know. I just want everyone who uses Benzodiazepines to at least give it a try as an anxiolytic. I really feel that a lot of people experiencing stress would be satisfied by Clonidine if they gave it a shot, but that's just my opinion.