I really don't need any additions to my collection of baitcasters, but wouldn't mind doing some further upgrades to my Sols and Alphas.  Does anyone know where I can purchase an SV spool for them?  TackleTrap doesn't have any.  Also, if anyone has made the switch to one of these spools, how much of a difference did it make?

3 hours ago, papajoe222 said:

Also, if anyone has made the switch to one of these spools, how much of a difference did it make?

How much in term of what? Distance?

May be not and you might even loose some too. The SV spool only help when you try to cast light weight lure. I use alphas 103 spool (12lb/100yds) for general purposes with 12lb Copolymer but use SV spool(10lb/90yds) with 8lb copolymer for lighter weight lure. 
I do have extra SV 105 spool if you really want it.

Japan Tackle had some Alphas SV spools last I checked. I had one in an R edition and presently a Sol. It's a nice upgrade over the stock spool but a bit short on line capacity. Good light line spool, as others have mentioned. I run 12 lb. Assassin on mine. 

Another option for you is to buy Daiwa SV 105 spool direct from Daiwa or tackle trap. It is basically the same as alphas SV.

https://tackletrap.com/index.php?main_page=product_info&products_id=10185

If you want mine that would be 55 shipped with PayPal F&F. I sold my alphas SV and as of now I can no longer using right hand reel. 

Here's the Japan Tackle Link for Daiwa spools, including the 105.  

Jun at JT has excellent English.  

Daiwa - Spools, casting reels - Tuning Parts (japantackle.com)

 

Regarding how much difference, I put the Roro-X (fixed brake rotor) spool on a Steez, and the 6-g spool will reliably cast 2-g jigheads to 100' - that's with a spool capacity of 100 m PE#0.8 X-braid.  

The difference is night and day if your goal is fishing UL lures.  

The SV function is more important casting greater weight - SV adds extra inertia-brakes at spool start-up.  Lightweight spools and light lures really don't have much inertia or overshoot tendency starting up - good mag-brake for mid-cast wind backlash is everything you need.  

 

Ray's Studio from Thailand makes SV-spools for Daiwa as light as 9 g - you can find them on ebay.  I have one of those in the mail, too - matching it with a multi-niche BFS bass rod that's rated for 1/16- to 5/8-oz lures - that's a wide range and will need the SV complication. 

 

 

I fished Steez/RoroX and 3-g plugs for the first time yesterday, and was casting them completely across the tide pass I was fishing -  

- dug for this photo, different day, but I was casting 3-g plugs from this hard pack into the grass on the other side - had the wind behind me, so didn't need brakes for anything, and the outfit made for gratifying fishing.  

Ichiban Tackle is worth a look too, check their used gear.