I've battled hairloss throughout my life and especially while on cycle. Every cycle I run I take that chance of really messing up my hairline so I always watch it very closely.
I can tell you some of the products I've used in the past that have worked for me. However I don't have much experience in regards to your specific question; hairloss during PCT.
i've used Rogaine in the past. I liked it as it definitely made my hair thicker and fuller looking. However, Rogaine does nothing for blocking DHT to the scalp. If we look at MPB and how it slowly robs the scalp and hair of essential blood, vitamins, protein, and a slew of other things. When those essential elements aren't present the hair follicle decreases in size and thus makes it easier to fall out. By adding Rogaine you are strengthing that hair follicle thus making it harder for it to fall out. There is much more to Rogaine than just what I've explained but in essence applying Rogaine during cycle thickens the hair follicle and if anything will SLOW hairloss. There are reports suggesting that Rogaine can regrow hair but ultimately that's not what we're discussing. Rogaine is however a treatment that once started needs to be continued but I've started and stopped plenty of times and if anything I believe Rogaine has essentially helped my hairloss because I've taken it during some of my cycles.
Nizoral shampoo is said to help block DHT from the scalp. As I'm sure you know there are different strengths of this shampoo. I believe you can get 1% as an OTC and 2% and 5% with a prescription. I've always run this shampoo with an EOD frequency while on cycle. On the off days I substitute with T-gel shampoo. Both shampoo's should be left on the scalp for roughly 3-5 minutes.
Propecia has also been an avenue I've gone down. I was lucky enough to get the doctor to prescribe me 5mg tabs and my insurance covered the cost. Breaking the 5mg tablets into 1/4's helps save on money. I noticed some rough sides with this medication but honestly I worked through them in hopes to see benefits. I was on Propecia for roughly 2 years before I discontinued use. Post medication I actually read some pretty disturbing side effects that have now been linked to Propecia and that was enough for me to never try it again.
SPIRO might be something for you to look into as it does great things for hair loss in some individuals but there are also plenty of side effects that go with it. SPIRO has been known to lower T levels and se individual's have actually experienced gyno like symptoms while taking SPIRO. There is a long outstanding debate if Topical SPIRO goes into your blood stream enough to change hormone levels in the human body. I can tell you without a doubt that topical SPIRO does in fact alter hormone levels. On the positive side SPIRO can be great when running AAS. With most cases Synthetic Teatosterone is being added to the body, hence adding SPIRO can't lower T levels to make a difference. As for an estrogen build up if the individual is consuming and AI they shouldn't experience gyno like symptoms. Sadly, for you and you being in PCT SPIRO might as well be counterproductive when it comes to getting your testosterone to baseline.
Vitamins have been known to help strength hair. B vitamins to be specific. Fish oil is also good for hair as well.
Your best bet is to load up on vitamin C as it reduces cortisol. However I doubt your hair loss is being caused by cortisol levels but it can't hurt to add lots of vitamin C as its water soluble and any extra will be urinated out of the body. Nizoral shampoo would work with DHT and that's most likely what's causing your hairloss.
Like I said above I'm not to familiar with hair loss during PCT. For all I know you might already know most of this information but I figured I can share the small amount of information I've gathered over the years. Research hairloss in your search engine and there's a ton of forums that discuss different methods and products. Most don't work but some do.
Good luck brother and try not to stress. If it happens it happens. Shaved heads are in these days