Options for long term storage of helium?
In my experience, for small quantities in laboratories helium usually comes compressed in cylinders. Except possibly in the case that you require extremely high purity, I don't see why helium couldn't be stored for long periods in this form, it would be relatively safe and would avoid the need for refrigeration.

I don't know what sort of quantities you are thinking about, but it seems that you can get big cylinders. For example the largest cyclinder size available from BOC gases, a British company, is 194.7 $m^3$ filled to a pressure of 300 $bar$ (source: BOC website).