Not so much track spikes but sleepers, rail and chairs for G scale can be brought from Tenmille'
http://www.tenmille.com/GScaleTrack.html
Tenmille G scale rail is code 332, but the foot is narrower compared to LGB/PIKO/ART/USAT.
It can be joined to other makes using their GS011 fishplates, or you could use railclamps if you file the wider foot of the 'standard' rail to that of the Tenmille, as Neil Robinson has.
The layout at Ipswich Transport Museum uses this track (although the points are LGB, joined with GS011 as above) and it works fine with LGB profile wheels....