"i stopped there on my last drive through mexico trying to get the pharmacies to sell me some valium, but it was a no go."

? you couldn't get Valium from a Mexican Pharmacy?
When they said you need a perscription, your supposed to ask if they know a doctor, they can usually point you in the direction of one less than a block away, or there is often a doctor on hand in the pharmacy.
No messy checkups, or paperwork. A $5er will usually cover as many prescriptions as you want.