This question is similar to this, but that one only references MD5 collision demos.
Are there any actual SHA1 collision pairs of arbitrary messages known so far ?
There is an example in Collision Search Attacks on SHA1 paper by Wang, Yin and Yu, from 2005, but just for weakened, 58-round version of SHA-1. (The full, official SHA-1 performs 80 rounds.)
3 A collision example for 58-step SHA1
h₁ = compress(h₀,M₀) = compress(h₀,M'₀)
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h₀: 67452301 efcdab89 98badcfe 10325476 c3d2e1f0
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M₀: 132b5ab6 a115775f 5bfffffd6b 4dc470eb
0637938a 6cceb733 0c86a386 68080139
534047a4 a42fc29a 06085121 a3131f73
ad5da5cf 13375402 40bdc7c2 d5a839e2
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M'₀: 332b5ab6 c115776d 3bfffffd28 6dc470ab
e63793c8 0cceb731 8c86a387 68080119
534047a7 e42fc2c8 46085161 43131f21
0d5da5cf 93375442 60bdc7c3 f5a83982
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h₁: 9768e739 b662af82 a0137d3e 918747cf c8ceb7d4
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Table 2: A collision of SHA1 reduced to 58 steps. The two
messages that collide are M₀ and M'₀. Note that padding
rules were not applied to the messages.