There are Several ways to do that.
For LootTables, you can either write them yourself, or use a Tool Aviable:
I recommend reading up on LootTables:
As For NBT files:
I ALSO recommend to read up on it:
As for how to get/make them, there are enough ways.
- First: As I said, BO3Tools can Export them with the Object in itself.
As I said, I dunno how BO3 Tools exactly works. As I dont use any more Features than to just Export Objects. (And Even that I dont use anymore).
- Second: You can get specific NBT files from places.
I dont know any repositories, but as this are Files, you can Share them. So you dont exclusively need to make your own.
- Third: You can Create your own.
NBT Files are just a specific FileFormat. Any tool capable of Editing them should also be capable of creating their own. And If you take a look at the MineCraft Wiki you can easily guess/read up how any NBT file should look like.
- Fourth: You can extract them directly from your World or Schematic.
If You read up on NBT files, you can easily see that minecraft stores almost everything in NBT format. WorldEdit schematics are the same. If you export something in WE, you can just cut out the NBT tags you need.
You will need anykind of NBT editor to make tweaks, (google it, …).
There is also a Tool here on the Forum that enables you to Convert your Schematics with NBT data to Objects.(And NBT files)
And how to make them work with your Objects: