The ink bottles equivalent to the Epson 502 hold 127ml (Black) and 70ml (each Cyan, Magenta, Yellow). There is a 4 pack of compatible ink bottles for $24.99 here:
https://123refills.com/cic/product.php?product=Compatible+ink+bottles+Multipack+for+Epson+502+-+4+pack
Below are the Epson equivalent items and capacity:
Manufacturer Part number Description Common name
Epson 502 black Black Ink Bottle; 127ml. 7500 Pgs Epson 502 Black Ink Tank
Epson 502 combo Combo Pack; 1ea K/C/M/Y Epson 502 Combo Pack Ink Tanks
Epson 502 cyan Cyan Ink Bottle; 70ml. 6K Pgs Epson 502 Cyan Ink Tank
Epson 502 magenta Magenta Ink Bottle; 70ml. 6K Pgs Epson 502 Magenta Ink Tank
Epson 502 yellow Yellow Ink Bottle; 70ml. 6K Pgs Epson 502 Yellow Ink Tank