Store wise you will be out of luck I don't know any specific stores that sale that brand new motherboard in the US. Your best bet would be Amazon, Ebay maybe even this site I can take a look around and get back to you.
I would take it back apart and check all of your connections I seems that your accelerometer isn't working. Its soldered on the motherboard so it can't be unplugged, but if some of your cables are loose or bent it can cause some strange problems like this.
Whats app should be able to be recovered just by logging back in. Everything else could be gone forever unless you had a sd card in the phone or used something like google photos that backs up your photos every time you take them.