Generally, you give them a certain amount of cc's per feed, and you want the crop to be full, but still soft. should be firm and look bloated almost, they should look stuffed and lopsided
These pictures may help - the moluccan, the white one, is full - so a stuffed crop. The grey is almost empty, see how it's just barely a bump?
I've never hand-fed a lorikeet, but if I recall correctly they're a little larger than a green cheek, maybe quaker parakeet sized? We used to feed our Quaker's 15-20 cc's per feed. Can you post a picture of your baby, with the crop full, and we can advise you specifically if s/he's full?
A photo would also help with getting a gauge on his development, relative to his age, so we can help with keeping him warm as well.
I understand what you're saying about the pet industry being...i dont want to say poor, but not as... compassionate? I've met many members who come and go in my years on forums and most from South East Asia, especially the Islands, all say the same - many birds are wild caught, are poorly cared for, and people are more concerned with making money than caring for birds or making sure they're healthy. It's a lose-lose situation, as many people's sole income is based on selling these birds and they can come from a very impoverished situation
Kudos to you for taking this little one in. It's not easy to hand-feed, and I've never fed a Lorikeet, so I can only advise based on my experience. We're here to offer all the help we can. One of our members, Kate, is well versed in caring for Lorikeets and I think she has hand-fed some before. I'll ask her to check out this thread and see what advice she can give you.