@am36 Thanks for reaching out!
Unfortunately, we do not carry replacement tent bags for our tents. The dimensions of the Camp Dome 4 tent bag are 8.7" x 27", which gives you a volume of right around 26 liters. Your best bet would be to purchase a size large (30L) stuff sack similar to this one, which should fit your tent, fly, and stakes, with no trouble. The poles will likely be too long for a stuff sack, however, and will need to be carried separately. The other option would be to purchase a duffel bag like the 60L REI Co-op Roadtripper Duffel. The dimensions of that duffel bag should allow you to fit the tent, fly, stakes, and the poles inside diagonally. You will have extra space in a duffel bag of that size, so that is something you will want to consider.
I hope this helps, happy camping!