my husband is coming to stay with me. how can i get invitation letter for a s1 or s2 visa for him?

Abigeal, you can write the invitation letter on your own. It should include the following information:
1. His name, sex and birth date
2. Why he comes, when he comes and leaves, where to stay, relationship with you and who covers his expense during his stay.
3. Your name, telephone number, address and signature.

Please do not prepare your marriage certificate, copies of your passport and valid resident permit.