Online resource for downloading gene variant data?
Seems your variants are all possibly harmful mutations to human genes, in that case ClinVar can be quite useful, it returns hits to all your variants except L747_T751delinsP. I have never used the ClinVar API so I'm afraid I can't vouch for how easy to use that is.

When ClinVar doesn't have the variant (or info about it) you need you could search EBI to see if other sites have information for this variant, when queried with L747_T751delinsP EBI actually shows us that it has been entered into Reactome twice. (welcome to the mess that is sequence annotation!).

This might be outside of your scope but if you have an interesting variant that you cannot find information on you could try to find the most similar (known) variant using BLAST.