Welcome to- The Fountain Pen Community!

I made my own Vac' tool, out of a block of Teflon, just chuck it in a Mill-vise, but then I'm not A-typical of the average person either.
If you need to buy one the $40 aluminum blocks look pretty decent, work on both sizes too, I've seen one model with Hex-head screws and another with a large thumb screw [the latter being much harder to come by and may not hold as well].
The hand tools are preferred to the blocks by most restorers, or so I've read, usually @ $30 each size you can sometimes get a price break on buying both sizes at once or @ $50 for both.

Fare warning:
In many cases you're going to need more than just the Vac' tool, things like...
sac scrapers to remove the ossified sac that often sticks and hardens like rock to the inner barrel walls,
pellet pusher/probe combo,
pellet remover of some sort, something to get the old pellets out with without damaging the delicate pellet pockets [there are a few different options here on how-to],
possibly some Parker Vac' lube to keep the diaphragm from twisting against the barrel when re-installing the filler unit,
X-acto knife or similar sharp/fine edge to cut the new diaphragm to the inner collar once installed over collar to the correct length,
make something to use as a stuck diaphragm pusher [when running into that as I have already],
padded section pliers to remove sections for proper cleaning and stuck sac removal,
a bore light such as used to inspect firearms chambers/barrels,
a set of brushes like test tube brushes that fit the inner barrel walls [soft bristle or nylon brushes only, never use metal brushes like brass or stainless as they'd tear up the plastic. I just use bore brushes for firearms since I have hundreds of them already] and so on...

In some cases, if the old diaphragm isn't stuck and welded to the inner barrel walls, you can forgo some of these tools such as scrapers [I use old dental picks, one in particular has an angled "spoon" end on one side that's perfect for this].
You can even spit on the new diaphragms to "lube" them for proper insertion and that often works in a pinch.
You can bypass a bore light and use a small LED flashlight in a pinch too, but a bore light works so much better.
I already had most of these tools from my work as a Master Gunsmith, the others I've made myself.
One source for the tools is Tryphon Enterprises [in the U.S.], another is Wood Bin [in Canada and yeah I know a name like "Wood Bin" makes people think cabinetry and "wood-working" but they sell pen tools & supplies] and Wood Bin has a great starter kit including diaphragms for under $100 w/o S&H.
If all else fails, others that already have the tools and experience can install a new diaphragm for you.
The fact you have several Vacs' it's probably a good idea to make the investment in the tools and learn how to do this yourself, cost would add up quickly restoring many pens vs just one.
Get the right size diaphragm replacement [there are 3 sizes, or in the case of a Speedline filler it's easier to know which one since they all take the smaller diaphragm or the "Debutante". Also, they don't come pre-cut and need to be installed "properly" [i.e. not too long and not too short, something not all people restoring them take the time to do right!].

I've been doing massive research on the topic of Vacumtic restorations, on both the Vacs and the P-"51" Vacs, even made my own P-"51" nib puller so I can take out nibs without having to remove the front hood.
I've only recently gotten into this myself, already I'm good at it, the best restorations are done with patience, observation, and more importantly having the proper tools.
It's not rocket science replacing a Vac' diaphragm, but the above "issues" do crop up and as long as you have the right tools it's a relatively easy fix.
Nice thing about the Speedline or Lock-downs is the pellet retainers are part of the aluminum plunger, far more durable than the plastic cups on the wartime plastic collars/plungers that are more fragile and can break if not handled correctly.
If you break a plastic pellet retainer you might as well start shopping for a new filler unit, unless you use adhesive [ugh, the horror!] as "some" do [not me!!!].