The greatest resource I've found for what you are talking about is a website called RockAuto.com
(NOTE: I have no affiliation with or interest in the website or the company listed.)
Yes, they sell parts, but they have a lot more information than that available on their website.
Here's what I do ...
I go to their website and look up the vehicle in question (whether mine or someone else's I may be working on, whatever.) Once there, I find the part in question. Let's use your vehicle as an example.
Once I've found the vehicle, I find the part.
You'll notice the website has four O2 sensors. Each one listed has in parens the phrase Click Info Button for Alternate/OEM Part Numbers. So, click on the Info button and lets see what happens.
Here is a list of all the part numbers associated with your downstream O2 sensor. You can then take these numbers and cross-reference them using Google or your favorite search engine. You'll most likely want to put something like "O2 Sensor" along with the number, or maybe your car information (ie: 2008 Toyota Camry Hybrid <sensor part number>).
This may not always work, however, I'd give it in the neighborhood of 90+% of the time looking on here provides me with a part number I can use. Once you have the part number, you can use it to find your part at the best price possible.
On a separate note, I get you might like to get OEM O2 sensors for your vehicle. You can usually get replacement O2 sensors just or good or better than stock from the aftermarket. In most cases, Bosch O2 sensors are among the best you can buy (you usually pay a bit more than generic ones, but they are good). Why are they good? Because Bosch developed them. They know what they're doing. My main point with this is, don't be hung up on OEM parts. In most cases OEM is good. Does that mean it's better than everything on the market? By no means. Do not be afraid to shop around. You can usually do better than stock (or at least as good as stock) at a much cheaper price.