The only way to still get ongoing (security only) updates to 12.04 is to enroll in the Ubuntu Advantage program for your 12.04 boxes. (There are minimum numbers of "licenses" you have to purchase, however, which means you need to be willing to pay a lot for these services).
This is the only way to get the Extended Security Maintenance for 12.04.
Details Details can be found on Canonical's site.
Without Ubuntu Advantage, you will not get 12.04 ESM updates. (However, 12.04 questions will remain offtopic here on Ask Ubuntu - ESM is a Canonical offering, so support will have to come from them)
In many cases, you're probably just going to want to upgrade rather than pay for the support, as in some cases the cost is prohibitively expensive.