The GS Type 2 just uses a standard 5" weatherproof horn speaker that is very common and very cheap. Any generic 5" weatherproof horn speaker with an 8 ohm impedance will work fine with the bell, so you don't need to order directly from General Signals. This one's pretty much a direct match:
https://www.jaycar.com.au/5inch-horn-sp ... m/p/AS3180
Here's another similar one on Amazon:
https://www.amazon.com/Speco-SPC-5P-Spe ... 84&sr=8-19
You can get an even cheaper one in black if you prefer:
https://www.amazon.com/Pyramid-SP5-Weat ... r=8-2&th=1
Here's the EXACT speaker that Safetran Type 3 E-Bells use. It would also work in a GS Type 2:
https://www.parts-express.com/5-indoor- ... e--300-050
The only things you'll need to do are to remove the supplied mounting bracket and bolt the speaker directly to the bell's housing using the screw on the rear of the speaker. The Jaycar horn speaker (the first one listed above) is supplied with the screw fully exposed. However, the SPECO and Pyramid models (the Amazon offerings) have the screw hidden by a panel showing information about the speaker. Remove this panel to reveal the screw:
Horn Speaker Guide by
Christian Nolan, on Flickr
Then bolt the speaker to the rear of the sound board as shown here:
gs type 2 by
Christian Nolan, on Flickr
Note: mounting the Safetran speaker in a GS Type 2 may be a little more challenging, as it has a slightly different design to the other models.
The final thing to do is to insert the speaker wires into the speaker outputs on the bell's sound board as shown here:
gs type 2 board by
Christian Nolan, on Flickr
For the SPECO and Pyramid models from Amazon, you'll need to cut the 3.5 mm jack off the end of the cable and strip back the wires (with wire strippers or scissors) before inserting them into the bell's speaker outputs. You don't need to do this for the Jaycar or Safetran speakers though, as they already come with bare wire ends.
All of this is very quick and easy and should only take about 10 - 15 minuets to complete. This DIY approach ends up being a lot cheaper and easier than dealing directly with General Signals!