I lived without the guide for years, then found one cheap one day on ebay. New ones are expensive (as are all new parts). Keep in mind that you might not be able to have the guide (when and if you find one) mounted with the cold light. In any event:
The indicator is attached by two screws. You can easily make one from thin metal, plastic, wood, even cardboard. Here are the indicator mark measurements for the different size negatives, all from the LOWER of the two screw holes:
4 x 5--one inch up
3 /14 x 4 1/4--2 3/16" up
2 1/4 x 3 1/4--3 1/4 " up
2 1/4 x 2 1/4--4 1/4" up
35mm--5 3/4" up.
Keep in mind that the precision required here is not very great. Actually, you can enlarge all the smaller sized negatives with the head set at 4 x 5, although that doesn't make greatest use of the enlarger's light intensity. If in doubt, just fudge a bit on the side of a bigger negative.
On the condenser: again, you might eventually come across one used, but you're more likely to find the whole condenser head as cheap or cheaper, if you're patient. I would set the thing up and see if the chip actually shows up in the image. It might not.