Randy – Thank you for your response!
I finally got around to calling Rheem today to ask about purchasing a second anode. The rep said that a second anode is only available as part of an extended warranty kit specifically for their wholesale line of water heaters. Apparently Rheem does not sell a second anode for installation in their retail line of water heaters (available from Home Depot), which is what I am looking to buy.
Thus, I think my plan will be exactly as you described: Wrap the anode threads with Teflon tape before installation and then set a reminder to check the anode once per year.
Thank you again for your help! I’ll certainly be back to purchase a replacement anode from you when the time comes!