Kevin, you can buy Bayticol in SA - looking it up, I see its active ingredient is "flumethrin", which is from the same family of compounds as permethrin. It's an aerosol that you can spray your socks, gaiters and lower trouser legs with. I've found it to work well in SA - I've never tried permethrin so cannot compare.
Regarding trousers, naturally it comes down to personal preference. While I occasionally wear shorts if hunting in very warm climes, I do find that sunburn and thorn damage can be a game-changer. So mostly wear long trousers. I have a pet peeve about noisy fabrics - virtually all synthetic fabrics, no matter how fancy, are super noisy in the bush - swishing noise when walking and loud scratch noises when thorns scrape them. Soft, well worn cotton is hard to beat for stealthiness. While long trousers may catch on thorns, I find that tearing fabric is usually a lot quieter than tearing skin
I've settled on a local el cheapo brand which works great:
Jonsson work wear (see the olive option - the perfect bush colour.
The trousers are lightweight, have a semi elasticated waist so very comfy, straight-leg so no flapping legs to catch everywhere, and not too bad if they get wet. I see on the label they are 65/35 polycotton - so I guess partly synthetic... but they are very quiet. The best part is they are available for R150-200 (call it $10) in most co-ops and outdoor stores!! I bought a bunch years ago with the view that I'd use them hard and ditch them, even if they lasted for just one trip. I am still using the original pairs a good 8 years on. The oldest pairs are showing a few small rips but otherwise going strong.