Great idea for DIY projects.
Many LED flasher ICs are available.
If I were making some, I would buy high quality capacitors for it. Good ones are not expensive. That is the part likely to fail with age or due to temperature extremes.
I buy my components from Digikey and Mouser (mostly). There is no minimum order, and shipping is fast and reasonable.
BTW, the invisible 980/990 nm LEDs work just fine with all of my NV stuff, even though the NV specs indicate that 880-ish nm is the upper limit.
So, if you want to avoid the visible red glow from your flasher, you might wish to give those a try.
And, for what it's worth, your cell phone camera can probably see the IR. With that method you don't have to hide in the dark closet with NVG to confirm it works.
Haji and others use cell phones and digital cameras/video cameras to see IR light sources approaching.