how do you tell a male from a female in the rainbow lorikeets?

Answer 1

DNA is the most accurate, safest and most reliable way. You can't tell by looking at them.
There are mail order kits that take a few drops of blood that you get by clipping a toenail too short.
Here are some good sites
http://www.vetdnacenter.com/avian-sexing.html
http://www.vetdnacenter.com/
http://www.aviarybirdshop.com/dnamicro.htm
I hope this helps.

Answer 2

Visual sexing is not reliable and surgical or DNA sexing is necessary.

They are beautiful birds, have fun with them