Unfortunately there aren't a lot of Gba Flash Carts with a RTC (at least that are very common) and I believe that the last EZ-Flash with RTC was the EZ-Flash II.
Of course I assume that you are new to the whole "Flashcart Scene".
Here is a "old" list of where to buy them: http://gbatemp.net/threads/gbatemps-off ... ers.33039/ (please be aware some of these dealers might not be operational anymore)
You may considering getting an EZ FLASH IV. I am using it quite smoothly on my GBA SP.
Based on its good compatibility with gba roms and stability, i think it is worth a try.
I'm not a mod so I can't enforce anything, but as stated in the majority of the rules, don't bump age old threads. Especially 2 year old ones. As for the advertising, I have no idea; but yeah don't bump old threads.