I was banging heroin (and plenty of meth/coke in there) for 7 cumulative years and, needless to say, I know your pain.
The desperation I went to to hit was astounding. I went from my arms and hands to my feet and then my ankles and calves. And then my neck. And then my groin and crotch. Finally...you know where. Nothing could stop me. I'm done now (18 months clean!) and can look back on that with some horror.
Anyway, a couple things that I did as I was winding down and getting desperate:
Warm washcloths held on the space you're trying to find a vein. This can help them stand up.
Go up in needle size (or down in gauge). This helps blood flow back into the rig itself and the heftier needle can punch through scar tissue more easily. I used 30 gauge (31 if I was hitting my hands or feet) shorts for years but towards the end I "upgraded" to a 28 gauge long. I was able to find a few deeper ones in my arms that way (and when I say deep, I mean I sank most of the 1/2th inch needle into my arm to find it). You aren't limited to just the veins you can see or "think" are there. Veins run all up and down your arms, and most you can't see.
Somebody said this, but ROTATE THOSE SITES. I know it's exciting to find a reliable spot to hit after struggling and just go in for the kill on that ONE specific spot going forward (I was that guy for a long time), but trust me, you are in for a life of pain and disappointment if you do that. My rule was 3 shots into that one spot before I move on and give it a minimum of five days to heal up. 7-10 days would be even better, though I know that's not easy.
Also, get creative. I don't know if you want to constrain your use to your arms only (though that won't last, if you're at all like me), but there are decent sized veins that run back underneath your forearm. If you do a "bicep flex" type of pose and look where your elbow meets your arm on the inside, you're gonna see some pretty thick veins run upwards. I made use of those many times. If you hit those, you might be shooting AWAY from your heart, so in the wrong direction in a sense, but as long as you don't slam the plunger down I never had any problems.
Finally, if you're shaking too badly from dopesickness, pop a few units of your shot into your upper arm or thigh. Wait a few minutes for that small amount of dope to absorb and your shakes will get a lot better. Just don't make a habit of doing that and DON'T do it with a dirty, because skin popping with dirties can give you an abscess. (Honestly, you should never do anything with a dirty rig besides dispose of it properly, but I would be a hypocrite if I said that I "only ever used a rig once.")
Hope that helps! I won't comment on your situation, because I don't know it, but if you ever want to discuss any hardships or addiction in general then let me know.