How can someone in Pakistan get a free virtual Visa or MasterCard without a bank account?

At present, you cannot. A virtual card like MasterCard or VISA is tied into bank accounts, via the issuing bank.

There is no plausible method to obtain one without directly or indirectly becoming a bank account holder.

In Pakistan, in today’s date, off-the-shelve, pre-paid virtual cards or physical cards by VISA/MasterCard are not offered.