This is a great question for your son's teacher. Some teachers do maintain websites for their classes, and some include assignments and academic resources, such as spelling words.
 
If your son's school is located in the United States, you can get its contact information in SchoolFinder (if you don't already have it handy): http://www.education.com/schoolfinder/
 
In addition to getting the spelling words from your son's teacher, you might also visit Education.com's Activities section to find fun ways to work with him on his reading and writing: http://www.education.com/activity/  (Note: To find appropriate activities faster, be sure to select his grade in the right column of the page, and then the topic areas for reading and writing).
 
Education.com also offers Reading and Writing information centers:
http://www.education.com/topic/school-subject-reading/
http://www.education.com/topic/academic-subject-writing/
 
Hope all of the above resources are helpful to you.

It always helps to have a homework buddy.  Get the telephone number of another child in the class.  Whenever a homework assignment is left at school or important test information - you can get on the phone with your homework buddy and have him give you the information.  Actually it might be a good idea to get the names and numbers of two people.  This way in case one of them also forgot the homework you have a back up plan.

He can go on the schools web site and you can ask his teather to go to spellingcity.com and put there  spelling words on there and they cam play games with there spelling words to help them know ho to spell them.

Hi, Myssy.
 
Chances are you're not the only parent in this class whose child has this issue! I imagine your son's teacher would probably be willing to email you once a week with the spelling list. That way you would be sure to have a backup in the event that he forgets to bring the list home.