Human embryos do have immature gills, but they are reused to create ears, jaw, tonsils, thymus, parathyroids and the large arteries in the neck and upper chest. We could add extra pairs and try to turn them into actual gills, although that would require removing the aortic arch and forcing all blood through the gills. Connecting them to the pulmonary system is not possible, as lungs and gills need different pressures (that’s the whole reason we have two circuits). Maybe we could connect them in parallel to the aorta? That would only work as a backup, but with an adequate vasomotor system could do a nice job!
I don’t really think the Russian economy is any real bottleneck here; they have abundant natural resources, a densely-knit industry and even now still many trading partners. Ultimately the only realistic way to stop the war is a peace agreement, which is why people voted for Zelenskyy in the first place.