Magnesium gluconate would be worth trying. It's supposed to be good on the bioavailability scale... but I'm not sure if it would have the same effects of magnesium citrate per se. Because different forms of magnesium may provide the body magnesium, but they often have a "side-effect". And I believe this side-effect is often what determines what form of magnesium is used. For example, it's pretty common that milk of magnesia, aka magnesium hydroxide, is used for upset stomach. Obviously magnesium hydroxide provides the body with magnesium like any other form of magnesium, but in this form it has side-effects that magnesium citrate does not have. So I said all that to say that just because another form of magnesium may be bioavailable, perhaps even more so than magnesium citrate, that does not mean they will have exactly the same effects.
But here's my take on this whole thing as a whole: if you've taken magnesium citrate and have only had beneficial effects, why not keep taking it? Why be afraid of it? Many people take and continue to take over-the-counter and prescription meds with much worse side effects than magnesium citrate has!
Also, if we're now afraid of citrate from citric acid, will you avoid any food that has citric acid in it, including citrus fruits?
I don't see any reason to be afraid to take magnesium citrate if you've had good effects from it. Also, if you're willing to drink a can of soda pop (many of them happen to have citric acid in it), or eat an orange, or what not, then why be afraid of magnesium citrate?
Those are my thoughts. This kind of goes back to what I said earlier about a double standard with supplements. Many people wouldn't hesitate to take Tylenol for a headache, but Tylenol damages the kidneys (I believe). But magnesium citrate may have some undesired effects, so now people are afraid of taking it... see what I mean?