C A L E N D A R :)
If you are on Mamapedia, you have kids, so you must keep track of their doctor & dentist appointments, school functions, sports schedule, music lessons, etc., correct? Do you use a calendar for this? Plan some time to go through your calendar & write down every single birthday & anniversary that you know of - call people if you must (there is someone you know who keeps track of all of that).
Use a bright color to write, so it stands out from everything else you are looking at on a daily basis.
One of your errands (like grocery shopping, gas station, dry cleaning) can be card shopping - monthly, quarterly, even just annually. It might take 20 minutes or an hour.
You can get a box with dividers for the months - buy your cards a stack at a time (bring your list of birthdays to the store & spend time looking), fill them out, stamp & address them, then put them in the box in the appropriate months - now you just have to remember to pull them out at the right time & get them in the mail! Kind of like paying your bills - those go out on time, right? You can send them every week, or twice a month - people don't mind getting their cards early. But like you said, people "love to get cards" - it feels special that someone took the time to actually look for a card, use an actual pen to handwrite something, address it, buy a stamp, & get it in the mail on time. That takes a lot of thought, & it is very much appreciated.
Get a handful of "belated" cards too, just in case. :)
When you buy next year's calendar, sit down with the ending year's calendar & the new one, & copy over (again in a noticeable color) all of those birthdays & anniversaries. I do this every single year, and even started doing it for other family members (people call me all the time to ask whose birthday is coming up) - I would buy 5 calendars & fill them all in for different branches of the family, depending on whom it was for.
When I was a teen, I knew which aunts took the time to write to me, & I decided then that no matter what, I would be the aunt who took the time to send a card because receiving one was so nice. I now have 19 nieces & nephews, & let me tell you, that's a LOT of cards! :)