Countries have tax treaties with each other which allows citizens of A working in B to have favourable tax treatment (no tax/reduced tax/taxed like a citizen of B). I've found good documentation for tax treaties the US has with other countries, but not for any country A with B. Is there a place where I can find this information? Barring such a general database, is there information for tax treaties India has with other countries (primarily west European)?
The best place to start searching for the Tax Treaties is the relevant tax authority in the country you are filing the tax returns for.
For example in the US the documentation can be found in publications from the IRS and for India is from the Income Tax Department, which when searching for "tax treaty" on their site will yield 2 results, which I think refers to the same document in 2 different formats.
There doesn't actually have to be a treaty between any country A and any country B. Most countries, in fact, do not have treaties with most other countries.
You can most likely find the list of countries a country has a treaty with on that country's tax authority web site. Accidentally, that is exactly the place where you went looking for the treaties the US has with other countries.
Treaties (of all kinds) are always “held” (not sure about the proper English terminology) by one of the signatories so there is no central authority listing them all and no exhaustive global database. You might find a database of all treaties a state has ratified on the website of the relevant Ministry for Foreign Affairs and advice on your tax status on the website of the relevant tax authority but the quality of these websites varies widely.
Also, treaties are useful to deal with complex cases (property in multiple countries, international inheritance, etc.) and to avoid double-taxation in countries taxing citizens wherever they live (like the US) but in many cases foreign residents are simply taxed like locals by default. Some countries have also established favorable rules (the 30% rule in the Netherlands, imposition au forfait/Pauschalbesteuerung in Switzerland, etc.) unilaterally.