I don't have this issue, but, I know that some distributors like Amazon.com Vitacost have options to get automated shipments every month. I think Amazon.com even offers a small discount for doing so. I guess it will depend on what supplements you buy and where you purchase them.
For such things, I use a low-tech approach of setting reminders in Microsoft Outlook that repeat every month. I use such calendar reminders for numerous things - Filing Taxes, Doctor Appointments, Trash/Recycle Day, Birthdays, Valentine's Day, etc.