There are two Spuhr dealers in the USA. Tactical Night Vision Company and Mile High Shooting Accessories. I've purchased from both companies before and they're top notch. One offers a 5% discount for SH members (can't recall which)
There are four mounting points on the Sako TRGs with the folding stock option. One is underneath the fore end rail, at the very front. One is off to the left (or right I suppose, if you flipped the bracket) of the barrel up at the front of the fore end. I removed it because it's not very useful with the TRG bipod stowed with the feet pointing towards the receiver. The other two...one at the rear of the stock, accessible from either side, and one on the left just behind the bolt. This mounting point can also be flipped for right-hand use. This particular mounting point can be seen clearly in the initial photo I posted above.
They're all visible in the photo below. It's wearing a biathlon sling attached underneath the rifle and at the rear sling point. You can see the sling bracket at the fore end just behind the left bipod leg, and you can see the protruding offset sling mount just above the pistol-style grip.
If there was a recommendation, I would consider the Kinetic Research Group's ambi-extended mag release. The factory mag release is kind of small. The extended mag release makes it easier to drop the mag with either hand and installs a horizontal paddle accessible to either side of the trigger guard. The only problem I had was a small burr at the edge that catches the mag so it wore the finish off my mags. After taking a fine Arkansas stone to give it a <.003" radius or so and rebluing the mag, it appears the problem went away because there was no more wear. It was a 5 minute job. Drift out old pin (don't lose the spring!), insert new assembly, drift pin back in. I also dropped in a grind-to-fit recoil pad to make it a little friendlier. 308 isn't a punishing round, but I'll take any advantage I can get. Lastly, if you're going to use a sling, I'd recommend experimenting a lot if you're also running the factory bipod. It's a fantastic field bipod but it's very unforgiving against human flesh because the feet are very stabby. If you decide to stow the bipod on the rifle, as designed, you'll have to experiment with the sling so you don't draw blood when carrying the rifle around.