They are relatively expensive. I just had a quick look at their preferred Registrar list and checked a several of them for prices. EuroDNS was the cheapest of those I checked at $62. ($15 or so at Somali registrars but that price may only be available to the domestic market). I haven't bought any .so myself. I checked for NNN on a handful of obscure TLD a week ago for interests sake last week using Name.com. I may be mistaken, but as far as I can recall there were many NNN.so available for registration last week. And that I could bulk search them easily.
Gandi's bulk search seems to be working. 20 domains at a time though... There are NNN available at .so (according to Gandi). I only checked a small sample - I would guess 35% of the NNN remain. I ran Whois on a handful of the handful - of those 70% or so were registered in the last 18 months by folks in China.
Checked and generated by Whic http://whic.ru/en/free/download Statistics: 495 taken - 49,5% 437 available - 43.7% 39 domains Pending del. (irrev.) - 3,9% 19 domains Redemption - 1,9% 7 domains not renewed - 0,7% 3 domains not delegated - 0,3% Spoiler: All available NNN.so 012.so 013.so 014.so 027.so 031.so 032.so 034.so 035.so 037.so 039.so 041.so 042.so 043.so 045.so 046.so 047.so 049.so 050.so 051.so 052.so 053.so 054.so 057.so 059.so 071.so 072.so 073.so 074.so 075.so 076.so 079.so 081.so 082.so 084.so 085.so 087.so 089.so 090.so 091.so 092.so 093.so 094.so 095.so 096.so 097.so 101.so 104.so 105.so 113.so 118.so 142.so 143.so 146.so 154.so 174.so 178.so 185.so 186.so 194.so 195.so 196.so 198.so 203.so 204.so 205.so 207.so 209.so 212.so 213.so 217.so 218.so 219.so 224.so 228.so 230.so 237.so 240.so 243.so 249.so 251.so 253.so 260.so 262.so 264.so 271.so 274.so 275.so 276.so 280.so 281.so 284.so 287.so 288.so 289.so 290.so 294.so 297.so 301.so 304.so 305.so 307.so 309.so 312.so 314.so 319.so 322.so 324.so 325.so 327.so 329.so 331.so 336.so 337.so 338.so 340.so 341.so 342.so 343.so 347.so 348.so 349.so 352.so 354.so 355.so 364.so 371.so 372.so 374.so 380.so 382.so 384.so 385.so 386.so 387.so 389.so 392.so 394.so 395.so 396.so 397.so 401.so 402.so 404.so 405.so 406.so 407.so 409.so 410.so 412.so 413.so 415.so 417.so 421.so 422.so 423.so 424.so 425.so 428.so 429.so 431.so 433.so 434.so 435.so 436.so 437.so 438.so 439.so 441.so 443.so 446.so 461.so 462.so 463.so 464.so 465.so 467.so 469.so 470.so 471.so 472.so 473.so 474.so 476.so 479.so 480.so 481.so 482.so 483.so 484.so 485.so 486.so 487.so 488.so 489.so 490.so 491.so 492.so 493.so 494.so 495.so 496.so 497.so 498.so 504.so 506.so 507.so 509.so 514.so 523.so 532.so 534.so 536.so 537.so 539.so 540.so 541.so 542.so 547.so 549.so 553.so 554.so 559.so 560.so 562.so 563.so 564.so 566.so 572.so 573.so 574.so 576.so 583.so 585.so 591.so 593.so 594.so 602.so 603.so 604.so 605.so 607.so 608.so 609.so 612.so 613.so 614.so 615.so 617.so 620.so 621.so 623.so 624.so 625.so 627.so 629.so 631.so 632.so 634.so 635.so 637.so 641.so 642.so 643.so 644.so 647.so 648.so 649.so 650.so 652.so 653.so 655.so 657.so 659.so 664.so 667.so 671.so 672.so 673.so 674.so 675.so 679.so 680.so 681.so 682.so 683.so 684.so 687.so 689.so 690.so 691.so 692.so 693.so 694.so 695.so 696.so 697.so 699.so 702.so 703.so 704.so 705.so 706.so 709.so 712.so 714.so 715.so 716.so 719.so 725.so 726.so 727.so 729.so 731.so 732.so 734.so 735.so 736.so 737.so 739.so 741.so 742.so 743.so 746.so 747.so 749.so 751.so 752.so 753.so 754.so 756.so 759.so 761.so 763.so 764.so 772.so 774.so 781.so 782.so 783.so 784.so 785.so 790.so 791.so 792.so 793.so 794.so 796.so 802.so 803.so 805.so 807.so 808.so 810.so 813.so 814.so 816.so 817.so 819.so 821.so 822.so 823.so 824.so 825.so 826.so 827.so 829.so 832.so 833.so 834.so 835.so 836.so 839.so 840.so 842.so 843.so 844.so 846.so 847.so 849.so 851.so 853.so 854.so 857.so 858.so 862.so 867.so 870.so 871.so 872.so 873.so 874.so 875.so 879.so 891.so 892.so 893.so 895.so 896.so 899.so 902.so 903.so 905.so 906.so 907.so 911.so 913.so 914.so 915.so 918.so 921.so 923.so 924.so 929.so 932.so 934.so 935.so 936.so 940.so 946.so 947.so 949.so 951.so 953.so 954.so 956.so 962.so 963.so 964.so 967.so 970.so 972.so 973.so 974.so 975.so 982.so 984.so 991.so There are a lot of not renewed domains, they can be a near future drops. Attached .csv from Whic