Where to get more 'images'

Hi!
You could use any images, but it depends if you want to properly match lighting and camera perspective or not. Theorically, yes, but experience told me that matching lighting and more critically Camera view with a non-HDRi image proves a hit and miss. That's actually something I look forward to test with Substance stager, but that's another story.
Typically if your only concern is reflection, then check eack with "image as light" and in that case it's important that the image is sufficiently wide (eg 360 degrees) to act as a proper scene lighting. I guess there is an amount of trial and error to be had.

If you type in HDRi in the search bar of the free section of Adobe Stock, you'll find some suitable images
https://stock.adobe.com/uk/search/free?k=HDRi&search_type=usertyped

and if you type "360", you'll get another set:

https://stock.adobe.com/uk/search/free?filters%5Bcontent_type%3Aphoto%5D=1&filters%5Bcontent_type%3Aillustration%5D=1&filters%5Bcontent_type%3Azip_vector%5D=1&filters%5Bcontent_type%3Avideo%5D=0&filters%5Bcontent_type%3Atemplate%5D=0&filters%5Bcontent_type%3A3d%5D=0&filters%5Bcontent_type%3Aaudio%5D=0&filters%5Binclude_stock_enterprise%5D=0&filters%5Bis_editorial%5D=0&filters%5Bfree_collection%5D=1&filters%5Bcontent_type%3Aimage%5D=1&k=360&order=relevance&safe_search=1&search_page=1&search_type=usertyped&acp=&aco=360&get_facets=1

run some tests to see if you really need HDRi images for your purpose...

Hope it helps!