Update 2Your post is fine right here in the DIY forum as you are wanting to make a DIY repair of your reel.
But, there is a gear forum for accessories such as reels:
Lift Bags, SMBs & Reels
Discover the wonderful world of lift bags and surface marker buoys and reels for wreck diving, cave diving or otherwise.scubaboard.com
and there is a forum specifically for Dive Rite:
Dive Rite
Come and meet your Dive Rite reps here on ScubaBoard. Ask any question about their products. This is a Dive Rite only forum.scubaboard.com
My suggestion is to give Dive Rite a call, they have excellent customer service and can best advise on the size screw/bolt you need.
(386) 752-1087
The other option would be take your reel to a hardware store like a True Value or Ace Hardware...one with a selection of Hillman hardware drawers. Then find a bolt that will fit. My assumption if the diameter of the plastic bolt you have is 1/4-inch is that the threading is 1/4-20...that is a pretty standard size and readily available. My bet is the bolt is plastic so it will break before the hole in body of the reel does....if you don't have a hardware store with a good Hillman selection, then go to home depot and find the correct fit in a metal bolt and let me know....we have a store nearby my house that has an excellent Hillman selection and with the correct threading and bolt length, I am pretty sure I can find you a nylon bolt to mail out to you rather inexpensively.
-Z
DGX is out of stock.
Next stop- Home Despot