Replacement for 52 tooth chainring Ultegra triple ( 6503 ) 9 speed Hello It seems that the stock 52t chainring for a road triple ultegra 9 speed is on  back-order or has been discontinued. Is there a replacement that will fit and shift? 
This is for my wifes Trek and she is not one to be told " Just baby it a little on the up shift "  Thanks in advance for any and all help in this matter.
You should be able to replace your chainring this with any 9 or 10 speed chainring that is 110 BCD (which is the Bolt Circle Diameter for the spider on an ultegra triple crankset). 

Tiagra/105/ultegra replacement rings should all fit, as well as most 3rd party manufacturers replacement rings.  Make sure the ring you want to use as a replacement has ramps and pins so that it will work as well as the original.  Stick with shimano parts to be sure of the best performance with the ultegra drivetrain.