The quick release plate that was originally supplied with your tripod is the Manfrotto 200LT-PL plate.

It's a variation of several slightly different plates made by Manfrotto that fit the RC2 (formerly called Q2) quick release system.

The standard 200PL plate includes a removable "vhs" anti-twist pin for use with cameras, mostly video cameras but also some DSLRs, that include a second hole for an anti-twist pin.

Any plate that is "RC2" or "Q2" compatible should fit your tripod. There are many third party makers of RC2 type QR plates.

There are also newer Manfrotto plates that fit both the RC2 and Arca-Swiss type systems, such as the 200PL-Pro

Note that the Manfrotto RC2 QR system is their most common one, but they also have other QR systems, such as RC4 (410PL), RC5 (501Pl, 503PL), RC0 (hexagonal), Q6, 357, 384 (dovetail), 785, etc. Just looking for a "Manfrotto plate" might get you one of those others which will not fit the RC2 base on your tripod head.

Thanks; so it's proprietary to manfrotto, but manfrotto has some dominance over the industry there so it's also fairly common. Do I understand that correctly?

In the past, Manfrotto QR systems were more common than they presently are. Arca-Swiss type systems have increased in popularity in the last decade or two. But the Manfrotto RC2 system is still fairly widespread and no single system "dominates" the industry.

Also, please note that not all "Arca-Swiss" type plates fit all "Arca-Swiss" type receivers, either. There are slight differences in plate widths, the angles of the bevels, and the shape of the corners where the bevels meet the bottom of the plate that sometimes will prevent a specific plate from fitting a specific receiver.