A reputable parts supplier will have adequate information for guiding you to the part you need as long as you have your exact model number. It seems like you probably already have your exact model listed in your post already. Avoid any parts sellers that do not provide adequate information to identify the part you need. If they don't have this information by default, then it either means they are not very detailed oriented and/or know nothing about Macs.
Make sure to note the exact model of your Mac by clicking the Apple menu & selecting "About this Mac".
FYI, to replace the speakers will require you to completely remove all of the internal components since the speakers are located beneath them.