Poses? I have you covered. I have walked this road thousand of times xD
For quick 'I need a reference for the thing I have in my mind', its very useful one of this 'Body Kun' or Body Chan'. The originals are expensive, but in AliExpress there are a lot of other options that are also very useful:
For muscles I use the TBLeague models. I still have to get a female one:
Furthermore, you can take a picture of the pose, and use the jpg as reference in your favorite drawing program!
But If you want to model a character in a 3D program, you can use the models from CSP. Sometimes is difficult to pose them, so try to download some premade poses in the assets and move them a bit. Other solution is https://justsketch.me/ page. An online 3D poser. Yet another solution is DesigDoll. This program was created for referecing, so its your best 3D bet. If you pay the license you can save your model, otherwise you will have to design it everytime you need a model, but once you have ready a pose you can save a jpg of the reference, or export the 3D as obj, that can be read in CSP as any other native 3D, and you can use the 3D camera from CSP to further adjust your pose details! The best thing in DesignDoll imo? You can upload another 3D objects there, an use them for your pose, as swords, guns, cars, etc. You can download a free 3D model, upload it in DesignDoll, create your model pose, export the obj, throw it into CSP, draw you character -and here is the best- hide in the options the model, and leave the object to extract the lines! Try it!
But you need reference images because your poses lacks certain je ne sais quoi? Of course Google Images is your friend. For a more random practice you can check https://quickposes.com/en/gestures/random, or you can personalize a Pinterest account. But if you REALLY need something extra, go deep and buy poses magazines like 'BL Manga Pose Book Collection', 'Dara tto shita Pose Catalog 1', or others. There are tons in sites like https://www.cdjapan.co.jp/
Finally, if you want to only see an image on your PC without much problem changing your view, opening tabs, or whatever, try PureRef. Its a free program that opens a window that its always open above other programs, and you can throw, or open, different images from the internet for you to use as reference, without opening other annoying programs or tabs! Below there is an example of how PureRef works.
Hope this little tutorial had helped you in your ways around the poses world =D