If you look at your manifold your silver B and it has a plugged 1/8" port on it, then you can easily plumb in a side burner. Where you find the side burner is another question. I don't know if you can still buy them, but they would likely be cost prohibitive any way. You would be better off finding one from another grill or just finding another silver or gold C to rehab. They are reasonably common. You might even be able use one from the older Genesis 1000-5000 grills.
This manifold is from a Genesis 1000 and you can see the extra port with a plug in it. You would just remove that plug and put in a 1/8" male NPT to 3/8" male flare adapter which you would then connect to the line going to the side burner. If the side burner line has a 1/8" male NPT connector on it, then you simply screw that in and skip the flare adapter.
Don't forget to use pipe dope on connections where required.