I'd like to use my FN FNX-45 Tactical for hunting and in my state you can only have 8+1 rounds in a pistol if you use it for hunting.

Any states have such a thing? I assume the smaller FN makes are 10's but figured it would be worth asking.

If not what options do I have to make such a thing?

Your best bet is to probably make, or have someone make a block to limit capacity. 

Do you have access to a 3D printer?  If so, the solution is easy :)

No... If I did and had a clue how to use one, don't you think I would have just done that?

Let's play nice now children...

Then here's what I would do if you're the DIY kinda person:

Take something that sits inside the magazine spring that will block the follower from dropping further to allow a 9th round from being inserted.  Buy a spare mag base plate assembly from Midwest or the likes and experiment. I'd use something like Delrin ( https://www.mcmaster.com/#acetal-homopolymer-sheets/=15jvye6 ) or some other durable polymer for the physical block.  Cut to length on a bandsaw (or similar) by measuring where on the magazine body the base of the follower reaches when round number 9 is inserted and add some nominal length to prevent reaching that length.  Then bond the plug to the baseplate assembly with some sort of epoxy, reassemble, test live.

It should require very little strength unless you plan on dropping your mags frequently or somehow battering the rounds in.

By doing it this way, you don't have to muck with the follower and potentially introduce feeding issues.

Just my $0.02.

I was playing nice! I'm pretty sure he was just given me a hard time! That said, I just realized we have 20 or so 3D printers at work. I still have no idea how to use them LOL! :)

The device you suggest is already made by Magazine Blocks but they only offer it for the 15 round to make it a 10. The way the 10 round mags are designed, I dont think it would work because they are dimpled on the sides to keep the follower from going down past 10 rounds. BUT I may be able to modify a 10 rounder and add another dimple a couple rounds above the factory one.

Damn 10 rounders cost more than the 15's though :(

Careful dimpling the mags. Knocking on it too hard my torque the body out of square and thus might introduce fitment issues.

I think your easiest route is to go with the mag block method.  This way you can use an existing 15round mag, swap out base pads when you go hunting, and swap back when you want to go to the range/HD.

3D printers are rather easy to use.  The CAD software is not-so-easy.  If I get time, I'll draw something up for you in Solidworks/NX/etc. and export the STL to you.  STL should be all you need to print if you want to go that route.

I was going to suggest buying the Magblock part and then adding some epoxy to the end of it, lengthening it so you can block the mag down to the 8 rounds you require. If you use an epoxy like bedding compound I don't think you'd ever have any trouble with the Magblock malfunctioning.

You could also drill a hole in the Magblock and insert a piece of bar stock aluminum to lengthen it to your desired round count. Just a little shaping of the aluminum bar stock and that's easy enough.