I can feel another one is about to take the leap! You can get it from supermarkets, butchers - pretty much anywhere you can buy meat. I have also heard of this
stuff that looks GREAT but of course we can't get it here, many RAW breeders feed this stuff in the US. You want to get at least liver, kidney, green tripe (I just can't get it green over here) and hearts but you can add any other bits you can get like trachea, tongue and all those other gross sounding bits.