I do know that Causeway B&T here in Wantagh has as really good inventory of Shimano parts. I generally go to them first, as I really dislike having to chasing down parts I need for my own reels, let alone those I work on for others.
However, I also like Ebay for odd-ball discontinued parts. It's come thru many times for my needs. Just have to be patient with Ebay, because its so random. But you never know, what you need could pop up the day you look for it.
Example - I have a MINT Curado 200D5 that's probably 20 years old that really needed a gear set change. Shimano hasn't had inventory of those gears for ages. A really rare gearset, for sure. Once a week I'd check Ebay for parts I need for mine and some other guy's reels. It took more than a year and a half of checking, but sure enough, a brand new set appeared and I instantly bought them. Not cheap at $55, but they allowed me to put a $200+ reel back in my fluke lineup, and so I was fine with paying the fare.
By the way, the 200D-series of Curados is well known to be the toughest version of the Curado family that Shimano ever produced. They were replaced with the E-series after only 3 or so years, as the D's were far too heavy for the liking of the FW bass crowd for whom they were intended, and so never caught on.
But what was bad for the picky FW guys is good for us. H/D reels are what we look for, and the Curado 200D5 is EXACTLY the size and weight of the current 300-size Curado and Tranx reels that Shimano offers today. See, Shimano was ahead of its time with that D series of reels, but completely missed the mark trying to sell them to the FW crowd. Someone in Shimano's marketing department didn't do their homework, I guess.
Now about your Tek500 - I would completely break that reel down to the last nut and bolt, going thru it looking for those missing teeth. They went someplace and so you really do need to find them before putting that reel back in service. I suspect that's why the reel locked up. If I had to guess - a plastic tooth is stuck between the main and pinion gears. Possibly mashed into a main gear tooth groove.
