The newborn baby feeding cups look similar to an inverted bottle's lid. You can actually use the bottle lids if they are rounded - the Avent lids are very similar to the feeding cups I got with my Ameda pump. The main difference being that the official feeding cups have measurements on the side and have a lid. If you want the real thing, you could try looking at Medela's website:
Apparently you are supposed to angle it so that just a little trickles into the baby's mouth until he/she shows an interest; don't just pour it in. I found it a little tricky at first, but had success when I put her in her "bouncy chair" which holds her at a 45 degree angle which I have found ideal. Too upright and it all comes out because she hasn't figured out swallowing yet!