There is excellent billfishing on both the east and northwest coasts, although, as the other person that replied said, most is done on private boats. On the east coast there may be a charter boat available in some of the newer hotels in the Punta Cana area. There is absolutely nothing (except good fishing) at Cabeza de Toro.
On the northwest coast, from Luperon to the Hatian frontier, there is a chain of underwater banks, where the bottom comes up from anywhere around 400 fathoms to 30 fathoms, causing an upswell and billfishing is very good but, during the summer months, the water a little rough in the afternoons.
There, the best months for blue marlin are from now to September. White Marlin, later in the summer and early fall and sailfish from the fall into the spring months. Dorado always, Wahoo good in the winter months, Tuna in the summer, and always, occasionally, King Mackrel.
There is a two boat charter operation (a 42 Hatteras and the other, about 32 feet) running out of Puerta Plata. I can not remember the name of the operation but the Puerta Plata hotels should have it on file. The only problem is that it is a long, hard run from Puerta Plata to the area off Luperon, where the good fishing starts.
The last time I was in Puerta Plata, there was another charter operation advertising in the hotels to go out of Luperon, about a 1 hour drive from Puerta Plata. I have no idea what type of equipment they have or if they are bottom fishing or trolling.
If you read the fishing magazines, Barcardi Rum sponsered a tournament two years ago on the east coast. Salt Water Sportsman and Marlin Magazine editors participated in it and covered it in their magazines.
On the south coast (Santo Domingo, San Pedro de Marcoris, La Ramana), some of the hotels between Santo Domingo and La Ramana provide charters but, although you will pick up an occasional billfish, the fishing is not that great.
I have a 43' Hatteras, docked at Club Nautico de Monte Cristi (close to the Hatian border) that I am either going to sell or move to the east coast (no hotels close to Monte Cristi) to charter, because I have been transferred to
Central America.
Keep a tight line and remember to dropback on the strike.
Capt. Larry