Ask a Dog Vet and Get Answers to Your Dog Veterinary Questions
Dewormers are typically available over the counter at pet stores and some grocery stores. Pyrantel and Panacur (Fenbendazole) are the two common products.
As for a heartworm preventative, those are only available with a veterinary prescription. You could try to use an online pharmacy and explain your situation. They may send you some Heartgard to help out. They're not too strict with those products.
I hope this helps, let me know if you have any other questions.