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Here's a start, Felipe de Jesús Villanueva Gutiérrez - a Classical Romantic!
"Vals Poético" by Felipe Villanueva (1862-1893), a Mexican composer, violinist and pianist.
For more info on Felipe Villanueva -
The Mexican Romantics were mostly overshadowed by Carlos Chávez and the nationalist composers who followed him. I see you've already found Ricardo Castro.
Julián Carrillo (1875-1965) isn't really known as a Romantic, because he is better known as a modernist and a proponent of microtonal music (music using intervals smaller than half steps). But early in his career he composed in a Romantic style.
Here's his String Sextet, composed in 1900.
Also, I've played a fair amount of music by Mexican (and other Latin American) composers, because Camellia Symphony has an Argentine conductor. The first concert I played in that orchestra featured all composers from Spanish-speaking countries (not all Latin American, as there was one Spanish composer) and I later played an all Latin American concert.
Other than José Pablo Moncayo's "Huapango", which I mentioned in another thread, here are other Mexican pieces I can remember playing.
Danzón No. 2, by Arturo Márquez, which is probably the single most performed piece by any Mexican composer:
Sinfonía India, by Carlos Chávez, which is based entirely on Native American folk songs that Chávez recorded in northern and western Mexico.
Chacona a Chávez, by Enrique Diemecke, based on a chaconne by Handel. This piece was commissioned for the 100th anniversary of Chávez's birth. In the 1930s Chávez produced one of the best known modern orchestrations of Baroque music, a chaconne by Buxtehude. Diemecke chose to pay homage to Chávez by following in his footsteps and orchestrating another Baroque chaconne in a "Mexican" style.
Marcha de Zacatecas, by Genaro Codina, sometimes referred to as Mexico's second national anthem. You can definitely hear Central European elements in this. Codina was mainly a composer of dance music, and was from the state of Zacatecas, part of the northern region where German and Czech folk music were influential.