Factory 303 that's easy to source will probably limit you to highland. 150 and 180 gr soft points seem to be the general easy to find rounds. If you search long enough you may find other brands.
Contact your closest Service Rifle club as those guys shoot alot of 303 and should have an idea of where to get other brands. Other than that if you reload that will be the best way to go. You can tailor make your ammo.
Cheers.
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