Does anyone have a source on some of the factory PS90 accessories. I have been looking for the factory side rails and the factory sling but have yet to have any luck finding somewhere that has it. I know they have been discontinued but I was hoping maybe I'd get lucky finding some new old stock. Thanks in advance for any ideas.

I bought mine from Brownell's about 4 months ago, but they're currently showing out of stock.  They do pop up on Ebay once in a while also, but they're not cheap.  You could order through Midway (currently backordered), and wait for them that way.  

Or...

You could order them aftermarket, through Damage Industries.  They are an extremely high quality alternative, and they also offer a few configurations that the factory ones don't.  Look at the link below and see the side rails with the built-in sling swivel mounting point.  Rail space on a PS90 is scarce with an optic (and potential light) installed.  These could definitely come in handy.  

I did order the PS90 optics rail from them, which takes the place of the factory top rail, only it's about ~3/8" lower and thinner than the factory one, which places an optic at a much more comfortable level.

Damage is here:
http://damageindustriesllc.com/product-category/155

For the sling, you could find one of the above mounting points for the front of the rifle, and then drill your own hole in the rear / top of the stock for a Noveske recessed qd mounting socket.  They're about $25, easy to find, even easier to install, and rock solid.  Installing this was a breeze with a new, sharp drill bit. With this in back (and one of dozens of choices up front), you can run any 2-point sling you want.

http://www.shopnoveske.com/products/flush-qd-sling-mount

Here's mine - hope this helps!

http://www.midwestgunworks.com/page/mgwi/ctgy/fn-ps90-accessories

What is the back of that sling hooked up to?

A Noveske QD Swivel mounting cup - see the link above for details.  I drilled it into the top of the stock.  Not my idea originally - got the idea here:

http://fnforum.net/forums/fn-ps90-accessories-mods/55749-noveske-flush-qd-mount-ps90.html

what trigger do you have on your ps90?

That's an AMP Trigger

I have one on mine

I hate you. Stop costing me money.