Unfortunately no....there isnt. Not for severe ED issues.
This is our experience anyway. So, there are tools that can help get him an erection without too much issue (penis pumps) and there are tools designed to help trap the blood inside the penis when erection is achieved (cock rings) but the reality is that these tools will only help keep the erection for a very short time
Some guys will say "not true" but I put the question to them "Were they aroused at the time of using and do they normally have erection issues" If you use a cock ring, for example, on a penis that usually stays erect when aroused, then the cock ring is not actually helping you HAVE an erection, rather it helps make your current erection stronger and harder.
If the blood is just not flowing into the penis in the first place...or not staying in the penis, then cock rings and pumps can only do so much. They can only help to initiate and make the current erection stronger.
Cock rings will make an erection last slightly longer. But I ask any man who is wearing a cock ring..."After your orgasm, did the erection stay until you took the ring off - literally for half an hour or so after orgasm?" usually the answer is no, because you can lose an erection while wearing a cock ring. If your body stops sending the signals to the penis, the blood will flow out eventually if you are completely satisfied or completely unaroused or, in this case, have issues maintaining it in the first place. The blood will flow out slower...but within minutes, the erection may still be lost.
Unfortunately I do not know of any foolproof, guaranteed sex toys or sex tools that can give a man an erection and ensure he does not lose it. I think if this existed, someone would be extremely rich! :D I honestly think that the best thing you can do in your case is to use the pills from the doctor. As you have already mentioned yourself, most rings and pumps can only help to a limited extent if the problem is severe.
That's my personal opinion anyway, but I have some other advice:
Can his doctor not prescribe a different medication? I understand the issue with anti-depressant meds. As a female, they stopped me being able to orgasm, for almost a year. As soon as I stopped them, it came back! From what I understand though, there are now different medications and different types of anti depressant that do not have the same side effects with erection and loss of orgasm etc. Would it be worth seeing another, more sympathetic doc and asking to try different meds to find one that will help with pain but also not cause his erection issues?
May I also suggest trying vibrations? This is often overlooked for males, but When I struggled to orgasm, I could not get anywhere from manual stimulation, but powerful vibrators could occasionally work for me. Maybe ramping up the intensity of the stimulation he is used to, will help him "feel" more of that stimulation and it could really help him get somewhere. Its worth a thought. There are a few male vibrators available these days, but you could even try something like a Magic Wand.
Hope that helps. xx