Where are the Catholic priests and is it a sin to support the SSPX?

The sad fact of the matter is that there are only a few priests in the country that are fully Catholic. To answer your question about donating to the SSPX after one has been made aware of their heresies, the answer is yes it is a mortal sin for one to obstinately contribute to the SSPX, and by doing so one is showing Jesus Christ that he endorses the idea that Buddhists, Hindus, Muslims and Jews can be saved without the Catholic Faith, which they promote in their books. 

Pope Innocent III, Fourth Lateran Council, 1215: "Moreover, we determine to subject to excommunication believers who receive, defend, or support heretics."

Actions speak louder than words.  Thus, one can say that he disagrees with the SSPX, but if he still contributes to this group, then his actions prove that he doesn't stand against their heresy but endorses it. If you were to move to St. Mary's you could pay tuition only (since this is required) but you could not give any donations to the school or a penny of financial support.  You could only pay the tuition fee, just like if you buy a book from them: you can pay the cost of the book, but you cannot supplement that with any additional money as a donation. The SSPX is, unfortunately, heretical and schismatical for its union with John Paul II.  It is heretical because it holds that heretics are Catholics (which is heresy) and that people can be Catholic and completely reject the necessity of Christ and the Church. It is also heretical for holding that the Catholic Church is apostate (namely, that the Vatican II sect is the Catholic Church).  The SSPX is schismatical because it holds that one can reject the solemn Canonizations of the man it believes to be the Pope.