Theres a wide range of on line stores you can get AM and all the other bits and pieces from. Some, like Sprue Brothers in the US, offer a wide range of stuff. But I think most guys will use a number of vendors for certain items, with perhaps one main one and then others for any other bits. Problem can be finding what out there for certain kits. You could go on searching for ever.
My main site is Hannants. When I want AM, I check there site. But I have learnt which other site to check for anything more specific, usually smaller ones that don't have the wide range of the large sites.
I don't know anything about air liners and I don't build in 144. I did a search on Hannants and it came up with a number of items, 2 of which are for a Revell 737-800, I assume the one you have.
www.hannants.co.uk/.../index.php
You should be able to find these closer to home. You will soon learn which sites are best for what items. If your looking for anything specific and your not sure where to look, someone here will be able to help.
I am a Norfolk man and i glory in being so
On the bench: Airfix 1/72nd Harrier GR.3/Fujimi 1/72nd Ju 87D-3