This is a question that comes up every so often. Most people say nothing is needed beyond a good quality diet of whole animals. Could you give the source recommending supplements?
My own opinion is that breeder females are likely to benefit from either a vitamin supplement or a baby chick added to the rodent diet every few weeks. After all, if a vitamin supplement is good for pregnant women, shouldn't it be good for breeding snakes? I have seen a couple of cases of rapid shedding (shedding every 2 weeks) seem to benefit from a vitamin supplement. And cases of mouth rot are known to heal quicker with a vitamin supplement than without.
I do not think that extra calcium is needed. There is plenty of calcium in rodent bones, and adding more calcium is likely to throw the calcium
hosphorus ratio off balance.
I don't have any brand of vitamin to suggest at this time. A decent cage bird multiple vitamin with A, C, D3, assorted B vitamins, niacin and ribofavin should be all that is needed, with a doseage of a drop or two inside a dead mouse once or twice a month.
On the other hand, if your snake is intended as a pet rather than a breeder, very likely no extra vitmins are needed.
Paul Hollander