For the isolators on the roof, I use to take the plastic insulation from cables. But you also can find
"real" isolators in N-scale on the market, by Sommerfeldt for example.
30. Isolators for the pantographs(diam 1,5 mm, length 2 mm). 31. Isolators for the roof cable.
32. One leaning isolator on the roof-construction.(diam 2 mm, length 2 mm). 33. Main circuit braker, of the modern art. (diam 2 mm, length 4 mm). 34. The Isolatorers on each side of the 33, with the same measures as for 30.
35. The upper part of 33. (0,4 mm pasteboard). 36. A long, thin isolator (diam 1,5 mm, length 3,5 mm).