You can find out your STOCK ROM code through dialing *#1234# and you can download from below links.If it asks for password then it is "samfirmware.com"(without quotes) or sampro.pl .
Download Links are courtesy of sammobile and samfirmware community.
FROYO :
1.I9003XXJL9 - http://www.fileserve.com/file/jf7HvgM/I9003_XXJL9.rar
2.I9003ZCKA6 - http://hotfile.com/dl/99699364/58a8b...ZCKA6.rar.html
3.I9003XXKA7 - http://hotfile.com/dl/104906620/d07f...XXKA7.rar.html
4.I9003XXKA8 - http://hotfile.com/dl/100569734/423c...XXKA8.rar.html
5.I9003XXKA9 - http://hotfile.com/dl/104942852/3384...XXKA9.rar.html
6.I9003XXKB1 - http://hotfile.com/dl/104985993/f064...XXKB1.rar.html
7.I9003XXKB1-CSC-DBTKB2 -http://hotfile.com/dl/108472094/caf2...BTKB2.rar.html
8.I9003XEKB1- http://hotfile.com/dl/103455459/5de3...XEKB1.rar.html
9.I9003XXKB3 : http://hotfile.com/dl/109632538/8b50...XXKB3.rar.html
10.I9003DXKB2 : http://hotfile.com/dl/112533344/d0ff...DXKB2.rar.html
11. I9003ZTKC1_ZZTKC1 : http://hotfile.com/dl/114690468/e631...ZTKC1.rar.html
12. I9003JPKD1 : http://hotfile.com/dl/115297948/cd1e...JPKD1.rar.html
13. I9003DDKB2 : http://hotfile.com/dl/118886369/41e2...DDKA5.rar.html
14. I9003ZCKC1: http://hotfile.com/dl/115955648/5e2f...ZCKC1.rar.html
15. I9003JBKE1 : http://hotfile.com/dl/120663910/f3ff...JXKA4.rar.html
16. I900XXKC1 (EUROPEAN) :http://narod.ru/disk/14574272001/I9003.ZIP.html
17. I9003DXKE1 : http://hotfile.com/dl/121540531/c22a...DXKB2.rar.html
18. I9003ZCKE1 : http://hotfile.com/dl/121547281/fcf4...ZCKE1.rar.html
19. I9003XEKE1 : http://hotfile.com/dl/121542297/63b4...XXKB1.rar.html
20. I9003DXKF1 : http://hotfile.com/dl/125254491/fc97...DXKF1.rar.html
LATEST firmware : I9003DXKf1 (ASIAN) :http://hotfile.com/dl/125254491/fc97...DXKF1.rar.html