Had an idea for 223 round or flat nose bullets for tube magazines. Has this idea come up before?

No.
Manufacturers can't meet current demand for spitzers. No demand for RN or FP.
Tube magazine for spitzers would need a spiral mag ala Remington 14/141. No demand to build.
Tube magazine rifles have accuracy problems beyond 100-150 yards. 223 is a longer range cartridge.
Save time and trouble and just find either a Browning BLR or a Henry Long Ranger. Have had my BLR since the 1980's and love it. Have never held a Henry. Henry should handle heavier bullets with its 1/9" twist vs BLR's 1/12".

Of my 12 lever actions, 3 are BLR's and one is a Browning 1895. These four have been my primary hunting rifles since 1974. I found that lever actions do not require a tube magazine to be accurate, handy, quick handling rifles.