From what I've seen, there doesn't seem to be a way for the interface to get ahold of item links directly. I've got the same situation as you do, with wanting to link loot for guildies sitting out, and ultimately I ended up modding Othesus' Examine window, changing the first search buttons as follows:
Code:
<Button LocalTooltip="lootchannel" Location="0,0" Name="lootchannel" OnPress="beginchatinput "/tc lootchannel "" ScrollExtent="18,14" Size="18,14" Style="/ButtonStyles.find.style">
</Button>
This way I examine the item, click the channel button, click the examine window icon (which pastes the link at the end of the line) then hit enter twice (once to put focus on the chat line, and the second to send it).
Yeah it's convoluted, but once you're used to it it goes pretty fast. Click click enter enter. I'd love to find a way for the code to get the actual itemid so I could paste a nicely formatted channel tell with a proper link straight from the loot window, but unless we get that data in an accessible way it'll continue to be kludgy without 3rd party out-of-game apps.