wunju is a bit of a time warp but they’re quite friendly.unlikely to be as cheap as online as they have rent and salaries to pay.
cash converters on kentish town road have some thigns occaisonally… 2nd hand.
cash converters near old street / bethnal green have a few things too … again 2nd hand.
and theres a place along hammersmith high street that have a few things too.
guitarguitar are in camden too , though their online store is better for non guitar things , you can request a demo and i think they may ship an item to the store if you have a few days to wait…
sxpro are not far from highgate. theyre quite high end but have elektron things too.
theres a store towards harrow / high barnet … forgotten the name
theres also one towards staples corner , a bit out the way bit its near a big shopping centre .
with all that said , juno , red dog and westend dj are probably the main ones worth visiting , westend may do a price match but it depends on the item.
find a copy of timeout london , theres a lot on beyond central london / oxford street / soho .