In Lincolnshire, there are many mechanical boxes & semaphores still around. Barnetby is the main obvious one, with dozens of semaphores controlled from Barnetby East & Wrawby Junction signalboxes. Also in the area is Roxton Sidings, between Grimsby & Barnetby, about a mile south of Immingham, which has a box, a couple of semaphores for either direction & mechanical gates. The Barton on Humber branch line has Barton Lane crossing box (Thornton Abbey station), Goxhill, Oxmarsh & Barrow Road crossing (both in New Holland). Grimsby has Great Coates Sidings No. 1, Pyewipe Road & Marsh Junction with semaphores on the Grimsby to Immingham Light Railway, but these see very little use as the line is only open as & when required. There are a couple of semaphore signals also still at Ulceby Junction on the Barton on Humber branch, but these aren't too easy to see from the station.
No signalbox on the Barnetby to Lincoln line, or Barnetby to Scunthorpe line have semaphores anymore, although traditional boxes still exist at Holton-le-Moor, Wickenby, Langworth, Elsham & Appleby (Wickenby does still have manual gates, though). Gainsborough Central on the Barnetby to Gainbsborough line via Brigg still has semaphore signals, as does Gainsborough Trent Junction (although Trent Junction isn't publically accessible). Also, Brigg & Northorpe still have gates (Only Northorpe's is mechanical, though, as Brigg's are motorised). Stow Park on the line from Gainsborough to Lincoln as well (Saxilby still has mechanical gates, too), & Swinderby on the Lincoln to Newark line with semaphores & mechanical gates.
On the Great Northern & Great Eastern Joint line, semaphores still exist at Metheringham (Blankney Signalbox), Scopwick, Sleaford North & Sleaford South. I'm not sure on the line south of Sleaford on specific locations, but there are some. However, Spalding does not. East of Sleaford, there's Heckington & Hubbert's Bridge with semaphores & gates, and also Bellwater Junction, Wainfleet & Skegness between Boston & Skegness (Wainfleet now has lifting barriers though). West of Sleaford, there's Rauceby & Ancaster.
Hope this helps.