yes! here is a link where you can donate through PayPal:
EDITED
I have the letter… he writes in his letter:
“And I also write in my own handwriting that this is a mitzvah of Pikuach Nefesh and it is a great mitzvah to support and help him with significant amounts so he should be able to carry on his holy work. With Birkas Kohanim with love. Gamliel HaCohen Rabonovitch”
How can i post it?
Sorry, You can’t. Maybe post an address to mail a check.