Micro Engineering makes bridge track in code 55 and 70. Either would take a little work to connect to Peco, but the 55 would be easiest. Just file the extra base off the Peco rail and use a standard code 55 rail joiner. ME code 55 track will accept almost any flanges, except some of the very large ones from the earliest days of N scale, such as Arnold's.
Or, you could use wooden ties and lay your own to whatever standards your road used. I've done this in two ways. First, you can use PC ties every inch or so, and add wood or plastic under them to match the wooden ties between. This requires soldering, but is a good place to practice, if you haven't done it before.
The second method is best for larger ties such as some roads used. Mine are ME HOn3 ties, which scale about 9x15 inches in N scale. For those I drilled holes, using a jig to get the locations the same on all ties, and spiked the rails with ME "Medium" spikes. Gut the spikes off underneath, superglue them in place from the bottom, and add other ties between as with the PC ties. This method avoids soldering, but if you're using Peco track for flange clearance, may not work.
Either of these methods make adding guards rails easier than on the ME track, whic on the pieces I've seen, required gluing the rails to the almost unglueable ties. I've never actually used the ME track I bought...
Finally, if you want to really keep it simple, and don't mind slightly shorter than normal bridge ties, just cut the pieces between the Peco ties and shove the ties closer together. That way you avoid all incompatibility issues, at the expense of perfect realism.
