does anyone know the losses of lend-lease equipment(if ac or tanks) delivered to the Soviet Union?
From table on p.182 of Geust and Petrov "Red Stars 4" (for US a/c):
14,985 delivered from US factories for Soviet account
150 lost in the US and Canada (mainly on ferry flights to USSR)
586 lost "after departure" (mainly at sea on ships).
Slightly over half, and later in the war most, of lend lease US a/c for the Soviets were delivered by the ALSIB route, ie. flown from Lower 48 through Canada to Alaska, then across the Bering Sea to airfields in the Soviet far east. P-63's were almost all delivered that way, and almost half of P39's were. As implied by above figures, the ALSIB loss rate was pretty low. Also remember most sea deliveries were to Abadan in Iran (some bigger planes were flown there too, across the S. Atlantic, Africa and Mideast). Those deliveries suffered low losses as well. Only ~8% of the deliveries were to North Russia by sea, which were the only ones to incur substantial % losses on the way, though the book does not break out those details unfortunately.
P-63's saw brief action on the Eastern Front but no air combat (per the same book). Most were retained in the Far East and saw more extensive use in the Soviet war against Japan in August 1945, although didn't see much air combat there either because there was little Japanese opposition. Only one air combat mentioned in Soviet accounts, AFAIK was 17th Fighter Regiment P-63 claim to have downed a Japanese Ki-27 (Nate) or Ki-43 (Oscar, apparently Soviet records differ) of several attempting to attack Soviet A-20's, on the last official day of the war, August 15, 1945. I know of no specific Japanese account, Japanese Monograph No. 151 (account of the air campaign compiled for the US occupations postwar) gives claims for several Soviet a/c that day and losses of "about 10" Japanese a/c to various combat causes in the whole campaign.
Joe