Most folks have several different local organizations that accept blood donations (the Red Cross and several others). Google will tell you what organizations are in your area. I donate to the Red Cross and at least one other organization on a regular basis. They all check hemoglobin, but some do not check hematocrit. As long as your hemoglobin is less than 20, most places will be happy to have your donation. If your levels are way up there, they may say something, but in most cases they just note the level and move on with the donation.
Most places will not take double red cells on the first donation. Just find a place and donate whole blood. That will knock your levels down to a more reasonable range. Regular donations will help keep the levels in check. Adjusting the dose a bit would help as well.