Some companies do offer this service.
yup, if u ask for a replacement card as well when u purchase
No, actually. Sim cards were created for SECURITY. Remember back when people were "cloning" (duplicating IMEI signatures to make calls on other peoples phones)? Can't do that now. If a replacement SIM is activated, the old sim is automatically DEactivated.
No two cards can be simultaneously active with the same number.
Furthermore, once deactivated, it can't be re-activated. At least not without some inevitable device is created for "wiping" or "resetting" a SIM.