I'm not sure that Mark's kits cover the entire rubber seals needed, but Auto Atlanta (AA) used to sell a kit with most of the rubber seals (if not all), which was a mix of OEM & repro parts, & IIRC it was around $800 - so not cheap.
Not sure that 914Rubber sold full kits, but they do have a series of parts. Mark's stuff is good & usually an improvement over factory seals' 1960's-70's technology & materials, which were often a foam rubber material which can actually hold moisture within the seals. Mark has also focused on parts NLA from Porsche, like the cowl seals.
Some OEM are still available from dealers & the Porsche suppliers around (Pelican, Eklers/Automotion, AA, GPR, Stouds, Einmalig, TC'sGarage, etc.) - & PCA gives you a parts discount at the dealers, & those other suppliers have specials/discounts/sales from time to time.
Also you can find NOS ones on here & CL etc. that folks are selling off.
It will be pricey to do all the seals - or even just the major ones, & will probably take using a number of sources, including Porsche, 914Rubber, AA & some of the other sources.
Budget-wise - it may be best to assess which seals are in the biggest need to replace sooner, & get those done first. Along those lines, the outer window scrapers/seals & the cowl joint seals tend to shrink - the former are still available in OEM (AFAIK) & 914Rubber Repros, but AFAIK the cowl seals are only at 914Rubber, then the door inner & outer seals & the F & R trunk seals are critical is very bad.
Also make sure to pull off your interior door panels to clean out any crud in the bottom & the drainage holes, so that it can properly drain, since some water gets in there even when new, & the drainage holes along the bottom of the door are there for that purpose.
Best thing is to get a 914 parts manual & list the part nos. you'll & prioritize them, then check off what you can get in that AA or other "kit" & what else you may need.
You can download a free pdf Adobe Reader 914 PET parts manual at the Porsche website here - look near the bottom for the hotlink ....
http://www.porsche.com/usa/accessoriesandservices/classic/Good Luck!
Tom
///////