you won't easily found modchip in retail stores place like http://www.mod-chip.com/ps2-c-22.html or other place just google it, can deliver you some good quality modchip.
if you talking about HDD, you either use NA Board on PS2 Fat, or External HDD on PS2 Fat/Slim either way, you need Hacked MMC with a loader to launch the ISO browser for your HDD.