Rubber feet usually come off easily with a nice flat item like a butter knife or something like that inserted at a slight angle, then slid around the edges of the foot. You can consider this method next time.
You might not have to reglue them. There might be easily enough glue to stick the foot back on afterwards.
I'm not entirely sure which part you need, but Ebay for refurb or used parts might be an option.
I have an HP envy 17" as well. No touch screen. Top left has been making clicking noises by the hinge/security cable location. I haven't heard any rattling so I've been lazy and putting off taking it apart and dealing with the minor clicking noise due to slight separation of the plastic pieces from the aluminium.