The Building London blog has blogged a lot about the wide dispersion of bits of the various London Bridges before, and here in Barking are a couple of granite blocks from Rennie’s bridge, or maybe not! Read on!
See https://buildinglondon.blog/2022/02/22/31-old-london-bridge-part-2/ but note these discoveries follow other’s leads, listed below.

So are they from London Bridge? Vic Keegan states that these blocks arrived in Barking, not from when Rennie’s Bridge was being knocked down and replaced in the late 1960s, but from Merrivale Quarry when it was abandonned in 2003!
“… many stones were left at Merrivale Quarry in Dartmoor and auctioned off on the internet after the quarry was flooded in 2003. Barking Council had the foresight to buy two of them and here they are.” (1) So they are NOT actually from London Bridge! 😀
Keegan also mentions “another turned into a large sculpture at Barking Abbey.” but it is not clear where that is. (2) Maybe he just means these.

Laura Porter at Londontopia also mentions these stones and their location … “And over in east London, stones are outside St Margaret’s Church in Barking.” 3)

And it’s definitely worth visiting the area for the ruins of the mediaeval Barking Abbey (4), and the Grade 1 listed St Margarets Church (5), especially if you are an urban / ‘pavement geologist’ as the walls have some very interesting stones! Interestingly the church is not, as first appears, built of Kentish Ragstone, but of Reigate Stone, or Firestone. (6)

Getting there:
Barking is easy to get to by public transport with a host of rail, overground and tube lines from central London.

References:
1) https://www.google.com/maps/d/viewer?source=gplus-ogsb&ie=UTF8&oe=UTF8&msa=0&mid=1keR5HrN8ZN6KLI4vz_QLTa4p0bM&ll=51.54173540847766%2C0.07986153939102625&z=15
2) https://www.londonmylondon.co.uk/the-london-bridge-that-went-to-america-well-some-of-it/
3) https://londontopia.net/columns/lauras-london/london-bridge-is-falling-down-a-history-of-london-bridge-and-where-to-find-old-london-bridge/
4) https://en.wikipedia.org/wiki/Barking_Abbey
5) https://en.wikipedia.org/wiki/St_Margaret%27s_Church,_Barking
6) https://www.essexfieldclub.org.uk/portal.php/p/Geology+Site+Account/s/St+Margarets+Church,+Barking
7) https://www.croydoncavingclub.org.uk/node/391