More P-40Ns were built than (by far) than all of the B-29s built in total, and about half the B-29 totals are post-war!
We sent more P-39s to Russia, than we did B-29s to Tokyo 
Let me put it this way....
We built more P-63 King Cobras than we did B-29s during WW2!
If anything, it's one of the more rare planes (numerically speaking) built by the US.
Mr. Krusty, you raised the topic, recently, in another thread about new planes, of some late-war myth regarding some late-war Japanese tin being "uber". As you recounted, skeptically, there's always some stories out there about some Ki-100 or other such ac being challenged by 16 Hellcats and sending 'em all home in a box.
You're correct, of course, to be skeptical of any such myth. However, I was able to find what I think to be the basis for the myth. Consider the following tale and tell me if you think an exaggerated version forms the basis for all these late-war Japanese Cyber-Oni ac:
Although only 1,400 N1K1-Js were built, codenamed George, due mainly to landing gear and engine problems, the George was probably the fastest, and most maneuverable Japanese naval fighter of the war. In the hands of a veteran pilot it was a formidable adversary, particularly the later models with four 20mm wing cannon. It possessed good range (1,375 miles) and although maximum speed was under 370 mph. its handling was sterling. Because the power of its Homare 21 engine fell off rapidly at high altitudes, it was of little use against high flying B-29s, but against F6Fs and F4Us in middle and low altitude dogfights, it was spectacular. In February 1945, a lone Japanese ace, Warrant Officer Kinsuke Muto, engaged a dozen F6F Hellcats, single-handed, while flying a George. He destroyed four and forced the others to break off.
These last minute heroics, however, were the beginning of the end of Japan's aviation industry. While her newer fighters proved too little and too late, Japan persisted in building twin-engined fighters such as the Ki 44 Nick, which, despite improvements, still was basically an obsolete heavy fighter on the order of the German Me 110, one that could not maneuver with its single-seat counterparts. The naval air program also continued down the same engineering cul de sac. As the war news became grimmer, Japan introduced yet another three man torpedo and/or dive bomber. Also doubling as reconnaissance machines, these newcomers, such as the Yokosuka D4Y Judy, were generally slower than enemy fighters and, due to a lack of escorts, suffered heavily, even though they had a top speed of 350 mph.
<end excerpt> That's from a slightly shabby source (Airpower Mag) and I disagree about the N1K2 being "most maneuverable (clearly wrong on the basis of turn rate) but I can verify the story from other, more reputable but less colorful sources - e.g.,
http://books.google.com/booksid=MuGsf0psjvcC&pg=PA288&lpg=PA288&dq=kinsuke+muto+N1K2&source=bl&ots=K4YCCfRF6G&sig=dBROzw_aDkO77XSgLQaBMsWnUQY&hl=en&ei=P4eCS-bFGMWInQfylfHDBw&sa=X&oi=book_result&ct=result&resnum=7&ved=0CBkQ6AEwBg#v=onepage&q=kinsuke%20muto%20N1K2&f=falseSo, imj, that's probably the real story behind the myth. Your skepticism is thus justified, for 4 of 12 Hellcats ain't 16 - though, credit Muto with a lot of skill and some big brass balls.
